diff --git a/build/docs/defining-binaries.rst b/build/docs/defining-binaries.rst
index fd155917a18..cb52870cbc7 100644
--- a/build/docs/defining-binaries.rst
+++ b/build/docs/defining-binaries.rst
@@ -148,15 +148,24 @@ directory, in which case we can use the ``SimplePrograms`` template
        'SecondProgram',
    ])
 
-The corresponding ``SOURCES`` must match:
+Contrary to ``Program``, which requires corresponding ``SOURCES``, when using
+``SimplePrograms``, the corresponding ``SOURCES`` are implied. If the
+corresponding ``sources`` have an extension different from ``.cpp``, it is
+possible to specify the proper extension:
 
-   SOURCES += [
-       'FirstProgram.cpp',
-       'SecondProgram.c',
-   ]
+   SimplePrograms([
+       'ThirdProgram',
+       'FourthProgram',
+   ], ext='.c')
+
+Please note this construct was added for compatibility with what already lives
+in the mozilla tree ; it is recommended not to add new simple programs with
+sources with a different extension than ``.cpp``.
 
 Similar to ``SimplePrograms``, is the ``CppUnitTests`` template, which defines,
-with the same rules, C++ unit tests programs.
+with the same rules, C++ unit tests programs. Like ``SimplePrograms``, it takes
+an ``ext`` argument to specify the extension for the corresponding ``SOURCES``,
+if it's different from ``.cpp``.
 
 
 Linking with system libraries
diff --git a/build/templates.mozbuild b/build/templates.mozbuild
index 6df5f1411e3..0a347091ce9 100644
--- a/build/templates.mozbuild
+++ b/build/templates.mozbuild
@@ -11,21 +11,23 @@ def Program(name):
 
 
 @template
-def SimplePrograms(names):
+def SimplePrograms(names, ext='.cpp'):
     '''Template for simple program executables.
 
     Those have a single source with the same base name as the executable.
     '''
     SIMPLE_PROGRAMS += names
+    SOURCES += ['%s%s' % (name, ext) for name in names]
 
 
 @template
-def CppUnitTests(names):
+def CppUnitTests(names, ext='.cpp'):
     '''Template for C++ unit tests.
 
     Those have a single source with the same base name as the executable.
     '''
     CPP_UNIT_TESTS += names
+    SOURCES += ['%s%s' % (name, ext) for name in names]
 
 
 @template
@@ -41,12 +43,14 @@ def HostProgram(name):
 
 
 @template
-def HostSimplePrograms(names):
+def HostSimplePrograms(names, ext='.cpp'):
     '''Template for simple build tools executables.
 
     Those have a single source with the same base name as the executable.
     '''
     HOST_SIMPLE_PROGRAMS += names
+    HOST_SOURCES += ['%s%s' % (name.replace('host_', ''), ext)
+        for name in names]
 
 
 @template
diff --git a/content/base/test/moz.build b/content/base/test/moz.build
index ec05b17e996..881e0fab9b0 100644
--- a/content/base/test/moz.build
+++ b/content/base/test/moz.build
@@ -17,8 +17,6 @@ CppUnitTests([
     'TestPlainTextSerializer',
 ])
 
-SOURCES += sorted('%s.cpp' % t for t in CPP_UNIT_TESTS)
-
 MOCHITEST_MANIFESTS += [
     'chrome/mochitest.ini',
     'csp/mochitest.ini',
diff --git a/content/media/compiledtest/moz.build b/content/media/compiledtest/moz.build
index 0da44099221..cd818e4de6d 100644
--- a/content/media/compiledtest/moz.build
+++ b/content/media/compiledtest/moz.build
@@ -9,8 +9,6 @@ CppUnitTests([
     'TestAudioMixer'
 ])
 
-SOURCES += sorted('%s.cpp' % t for t in CPP_UNIT_TESTS)
-
 FAIL_ON_WARNINGS = True
 
 LOCAL_INCLUDES += [
diff --git a/content/media/webaudio/compiledtest/moz.build b/content/media/webaudio/compiledtest/moz.build
index e584c2016a5..1cb059d6f48 100644
--- a/content/media/webaudio/compiledtest/moz.build
+++ b/content/media/webaudio/compiledtest/moz.build
@@ -8,8 +8,6 @@ CppUnitTests([
     'TestAudioEventTimeline',
 ])
 
-SOURCES += sorted('%s.cpp' % t for t in CPP_UNIT_TESTS)
-
 FAIL_ON_WARNINGS = True
 
 LOCAL_INCLUDES += [
diff --git a/dom/audiochannel/tests/moz.build b/dom/audiochannel/tests/moz.build
index 64304545b10..51ad846ebb8 100644
--- a/dom/audiochannel/tests/moz.build
+++ b/dom/audiochannel/tests/moz.build
@@ -8,8 +8,6 @@ CppUnitTests([
     'TestAudioChannelService',
 ])
 
-SOURCES += sorted('%s.cpp' % t for t in CPP_UNIT_TESTS)
-
 if CONFIG['OS_ARCH'] == 'WINNT':
     DEFINES['NOMINMAX'] = True
 
diff --git a/dom/canvas/compiledtest/moz.build b/dom/canvas/compiledtest/moz.build
index 6e3a66ea13c..062adb39637 100644
--- a/dom/canvas/compiledtest/moz.build
+++ b/dom/canvas/compiledtest/moz.build
@@ -8,8 +8,6 @@ CppUnitTests([
     'TestWebGLElementArrayCache',
 ])
 
-SOURCES += sorted('%s.cpp' % t for t in CPP_UNIT_TESTS)
-
 FAIL_ON_WARNINGS = True
 
 LOCAL_INCLUDES += [
diff --git a/editor/txmgr/tests/moz.build b/editor/txmgr/tests/moz.build
index 316d7a80b5b..e2c223466c5 100644
--- a/editor/txmgr/tests/moz.build
+++ b/editor/txmgr/tests/moz.build
@@ -8,8 +8,6 @@ CppUnitTests([
     'TestTXMgr',
 ])
 
-SOURCES += sorted('%s.cpp' % t for t in CPP_UNIT_TESTS)
-
 FAIL_ON_WARNINGS = True
 
 USE_LIBS += [
diff --git a/intl/lwbrk/tests/moz.build b/intl/lwbrk/tests/moz.build
index 8beb091cf2c..1770e50da27 100644
--- a/intl/lwbrk/tests/moz.build
+++ b/intl/lwbrk/tests/moz.build
@@ -8,8 +8,6 @@ CppUnitTests([
     'TestLineBreak',
 ])
 
-SOURCES += sorted('%s.cpp' % t for t in CPP_UNIT_TESTS)
-
 USE_LIBS += [
     'mozalloc',
     'nspr',
diff --git a/intl/uconv/tools/moz.build b/intl/uconv/tools/moz.build
index fa7756ae9a9..a10820eb333 100644
--- a/intl/uconv/tools/moz.build
+++ b/intl/uconv/tools/moz.build
@@ -6,8 +6,4 @@
 
 SimplePrograms([
     'umaptable',
-])
-
-SOURCES += [
-    '%s.c' % s for s in SIMPLE_PROGRAMS
-]
+], ext='.c')
diff --git a/intl/unicharutil/tests/moz.build b/intl/unicharutil/tests/moz.build
index 9820a2de05e..80fc3b2bc41 100644
--- a/intl/unicharutil/tests/moz.build
+++ b/intl/unicharutil/tests/moz.build
@@ -6,13 +6,9 @@
 
 XPCSHELL_TESTS_MANIFESTS += ['unit/xpcshell.ini']
 
-SOURCES += [
-    'NormalizationTest.cpp',
-    'UnicharSelfTest.cpp',
-]
-
 SimplePrograms([
-    "%s" % (fyl[0:-4]) for fyl in SOURCES
+    'NormalizationTest',
+    'UnicharSelfTest',
 ])
 
 USE_STATIC_LIBS = True
diff --git a/js/src/moz.build b/js/src/moz.build
index 6eb7736b19d..82ff6ff3669 100644
--- a/js/src/moz.build
+++ b/js/src/moz.build
@@ -423,12 +423,8 @@ else:
 if CONFIG['_MSC_VER'] != '1600':
     MSVC_ENABLE_PGO = True
 
-HOST_SOURCES += [
-    'jskwgen.cpp',
-]
-
 HostSimplePrograms([
-    'host_%s' % f.replace('.cpp', '') for f in HOST_SOURCES
+    'host_jskwgen',
 ])
 
 # JavaScript must be built shared, even for static builds, as it is used by
diff --git a/layout/style/test/moz.build b/layout/style/test/moz.build
index 96f7636f3c4..9f9b80fc883 100644
--- a/layout/style/test/moz.build
+++ b/layout/style/test/moz.build
@@ -4,12 +4,8 @@
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
-HOST_SOURCES += [
-    'ListCSSProperties.cpp',
-]
-
 HostSimplePrograms([
-    'host_%s' % f.replace('.cpp', '') for f in HOST_SOURCES
+    'host_ListCSSProperties',
 ])
 
 MOCHITEST_MANIFESTS += [
diff --git a/media/libcubeb/tests/moz.build b/media/libcubeb/tests/moz.build
index e7869a529ca..7bf057a1b1b 100644
--- a/media/libcubeb/tests/moz.build
+++ b/media/libcubeb/tests/moz.build
@@ -15,8 +15,6 @@ if CONFIG['OS_TARGET'] != 'Android':
     'test_sanity'
   ])
 
-SOURCES += sorted('%s.cpp' % t for t in CPP_UNIT_TESTS)
-
 LOCAL_INCLUDES += [
     '../include'
 ]
diff --git a/media/mtransport/test/moz.build b/media/mtransport/test/moz.build
index fd2c8fb29e8..e30a3da583c 100644
--- a/media/mtransport/test/moz.build
+++ b/media/mtransport/test/moz.build
@@ -23,8 +23,6 @@ if CONFIG['OS_TARGET'] != 'WINNT' and CONFIG['MOZ_WIDGET_TOOLKIT'] != 'gonk':
             'sctp_unittest',
         ])
 
-    SOURCES += sorted('%s.cpp' % t for t in CPP_UNIT_TESTS)
-
 FAIL_ON_WARNINGS = True
 
 for var in ('HAVE_STRDUP', 'NR_SOCKET_IS_VOID_PTR', 'SCTP_DEBUG', 'INET'):
diff --git a/media/webrtc/signaling/test/moz.build b/media/webrtc/signaling/test/moz.build
index 5ce5002546b..e2af3824e4b 100644
--- a/media/webrtc/signaling/test/moz.build
+++ b/media/webrtc/signaling/test/moz.build
@@ -12,8 +12,6 @@ if CONFIG['OS_TARGET'] != 'WINNT' and CONFIG['MOZ_WIDGET_TOOLKIT'] != 'gonk':
         'signaling_unittests',
     ])
 
-SOURCES += sorted('%s.cpp' % t for t in CPP_UNIT_TESTS)
-
 include('/ipc/chromium/chromium-config.mozbuild')
 
 if CONFIG['OS_TARGET'] in ('Darwin', 'Android'):
diff --git a/memory/mozalloc/tests/moz.build b/memory/mozalloc/tests/moz.build
index 6b265f5beb9..fc540a1d587 100644
--- a/memory/mozalloc/tests/moz.build
+++ b/memory/mozalloc/tests/moz.build
@@ -8,8 +8,6 @@ CppUnitTests([
     'TestVolatileBuffer',
 ])
 
-SOURCES += sorted('%s.cpp' % t for t in CPP_UNIT_TESTS)
-
 USE_LIBS += [
     'mozalloc',
     'nspr',
diff --git a/mfbt/tests/moz.build b/mfbt/tests/moz.build
index 48c2fde8e71..f7eb7db4b5f 100644
--- a/mfbt/tests/moz.build
+++ b/mfbt/tests/moz.build
@@ -37,8 +37,6 @@ if not CONFIG['MOZ_ASAN']:
         'TestPoisonArea',
     ])
 
-SOURCES += sorted('%s.cpp' % t for t in CPP_UNIT_TESTS)
-
 # Since we link directly with MFBT object files, define IMPL_MFBT
 DEFINES['IMPL_MFBT'] = True
 
diff --git a/mozglue/linker/tests/moz.build b/mozglue/linker/tests/moz.build
index 4d1468bcfa0..a42f3c9505c 100644
--- a/mozglue/linker/tests/moz.build
+++ b/mozglue/linker/tests/moz.build
@@ -6,9 +6,6 @@
 
 NO_DIST_INSTALL = True
 
-SOURCES += [
-    'TestZip.cpp',
-]
 SimplePrograms([
     'TestZip',
 ])
diff --git a/mozglue/tests/moz.build b/mozglue/tests/moz.build
index 7b8d5ef7376..47c4c333aff 100644
--- a/mozglue/tests/moz.build
+++ b/mozglue/tests/moz.build
@@ -6,10 +6,6 @@
 
 DISABLE_STL_WRAPPING = True
 
-SOURCES += [
-    'ShowSSEConfig.cpp',
-]
-
 CppUnitTests([
     'ShowSSEConfig',
 ])
diff --git a/netwerk/test/moz.build b/netwerk/test/moz.build
index c86196ed4ae..75e4ced440d 100644
--- a/netwerk/test/moz.build
+++ b/netwerk/test/moz.build
@@ -46,18 +46,12 @@ SimplePrograms([
 #    TestUDPSocketProvider',
 #]
 
-SOURCES += [
-    '%s.cpp' % s for s in SIMPLE_PROGRAMS
-]
-
 CppUnitTests([
     'TestCookie',
     'TestSTSParser',
     'TestUDPSocket',
 ])
 
-SOURCES += sorted('%s.cpp' % t for t in CPP_UNIT_TESTS)
-
 RESOURCE_FILES += [
     'urlparse.dat',
     'urlparse_unx.dat',
diff --git a/security/manager/ssl/tests/compiled/moz.build b/security/manager/ssl/tests/compiled/moz.build
index 6ed376dd9da..7aaae8b3df5 100644
--- a/security/manager/ssl/tests/compiled/moz.build
+++ b/security/manager/ssl/tests/compiled/moz.build
@@ -8,8 +8,6 @@ CppUnitTests([
   'TestCertDB',
 ])
 
-SOURCES += sorted('%s.cpp' % t for t in CPP_UNIT_TESTS)
-
 USE_LIBS += [
     'mozalloc',
     'nspr',
diff --git a/security/manager/ssl/tests/unit/tlsserver/cmd/moz.build b/security/manager/ssl/tests/unit/tlsserver/cmd/moz.build
index 416fb35a1c4..dd91bbbd0b0 100644
--- a/security/manager/ssl/tests/unit/tlsserver/cmd/moz.build
+++ b/security/manager/ssl/tests/unit/tlsserver/cmd/moz.build
@@ -13,10 +13,6 @@ SimplePrograms([
     'OCSPStaplingServer',
 ])
 
-SOURCES += [
-    '%s.cpp' % s for s in SIMPLE_PROGRAMS
-]
-
 LOCAL_INCLUDES += [
     '../lib',
 ]
diff --git a/startupcache/test/moz.build b/startupcache/test/moz.build
index 7d6a4e7f7cc..6531d0dc022 100644
--- a/startupcache/test/moz.build
+++ b/startupcache/test/moz.build
@@ -8,8 +8,6 @@ CppUnitTests([
     'TestStartupCache',
 ])
 
-SOURCES += sorted('%s.cpp' % t for t in CPP_UNIT_TESTS)
-
 EXTRA_COMPONENTS += [
     'TestStartupCacheTelemetry.js',
     'TestStartupCacheTelemetry.manifest',
diff --git a/storage/test/moz.build b/storage/test/moz.build
index 02d25832bab..8bcd80a1951 100644
--- a/storage/test/moz.build
+++ b/storage/test/moz.build
@@ -28,8 +28,6 @@ if CONFIG['MOZ_DEBUG'] and CONFIG['OS_ARCH'] not in ('WINNT', 'Darwin'):
         'test_deadlock_detector',
     ])
 
-SOURCES += sorted('%s.cpp' % t for t in CPP_UNIT_TESTS)
-
 LOCAL_INCLUDES += [
     '../src',
 ]
diff --git a/toolkit/components/places/tests/cpp/moz.build b/toolkit/components/places/tests/cpp/moz.build
index c5488e751fe..b7935de0d26 100644
--- a/toolkit/components/places/tests/cpp/moz.build
+++ b/toolkit/components/places/tests/cpp/moz.build
@@ -8,8 +8,6 @@ CppUnitTests([
     'test_IHistory',
 ])
 
-SOURCES += sorted('%s.cpp' % t for t in CPP_UNIT_TESTS)
-
 FAIL_ON_WARNINGS = True
 
 USE_LIBS += [
diff --git a/toolkit/mozapps/plugins/tests/moz.build b/toolkit/mozapps/plugins/tests/moz.build
index ab0d7f17dd7..f54b170f1fb 100644
--- a/toolkit/mozapps/plugins/tests/moz.build
+++ b/toolkit/mozapps/plugins/tests/moz.build
@@ -9,9 +9,5 @@ SimplePrograms([
     'GoodPlugin',
 ])
 
-SOURCES += [
-    '%s.cpp' % s for s in SIMPLE_PROGRAMS
-]
-
 BROWSER_CHROME_MANIFESTS += ['browser.ini']
 USE_STATIC_LIBS = True
diff --git a/toolkit/mozapps/update/tests/moz.build b/toolkit/mozapps/update/tests/moz.build
index 49688d73e71..4d7ba65816e 100644
--- a/toolkit/mozapps/update/tests/moz.build
+++ b/toolkit/mozapps/update/tests/moz.build
@@ -18,10 +18,6 @@ if CONFIG['MOZ_WIDGET_TOOLKIT'] != 'android':
         'TestAUSReadStrings',
     ])
 
-    SOURCES += [
-        '%s.cpp' % s for s in SIMPLE_PROGRAMS
-    ]
-
     LOCAL_INCLUDES += [
         '/toolkit/mozapps/update',
         '/toolkit/mozapps/update/common',
diff --git a/toolkit/webapps/tests/moz.build b/toolkit/webapps/tests/moz.build
index 943219eb9da..fff331de0c9 100644
--- a/toolkit/webapps/tests/moz.build
+++ b/toolkit/webapps/tests/moz.build
@@ -5,5 +5,4 @@
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 MOCHITEST_CHROME_MANIFESTS += ['chrome.ini']
-SOURCES += ['TestWebappRT.cpp' ]
 SimplePrograms(['TestWebappRT'])
diff --git a/toolkit/xre/test/win/moz.build b/toolkit/xre/test/win/moz.build
index e99c6d2cf97..8771a63e672 100644
--- a/toolkit/xre/test/win/moz.build
+++ b/toolkit/xre/test/win/moz.build
@@ -8,18 +8,10 @@ SimplePrograms([
     'TestXREMakeCommandLineWin',
 ])
 
-SOURCES += [
-    '%s.cpp' % s for s in SIMPLE_PROGRAMS
-]
-
 CppUnitTests([
     'TestDllInterceptor',
 ])
 
-SOURCES += [
-    '%s.cpp' % s for s in CPP_UNIT_TESTS
-]
-
 DEFINES['NS_NO_XPCOM'] = True
 
 LOCAL_INCLUDES += [
diff --git a/tools/trace-malloc/moz.build b/tools/trace-malloc/moz.build
index 9c754913242..f602d44d516 100644
--- a/tools/trace-malloc/moz.build
+++ b/tools/trace-malloc/moz.build
@@ -15,30 +15,19 @@ if not CONFIG['MOZ_PROFILE_GENERATE']:
 bin_suffix = CONFIG['BIN_SUFFIX']
 
 
-simple_c_sources = [
-    'leakstats',
-    'tmstats',
-]
-
-SOURCES += [
-    '%s.c' % s for s in simple_c_sources
-]
 SOURCES += [
     'tmreader.c',
 ]
 
-SimplePrograms(simple_c_sources)
+SimplePrograms([
+    'leakstats',
+    'tmstats',
+], ext='.c')
 
-simple_cpp_sources = [
+SimplePrograms([
     'bloatblame',
     'leaksoup',
-]
-
-SOURCES += [
-    '%s.cpp' % s for s in simple_cpp_sources
-]
-
-SimplePrograms(simple_cpp_sources)
+])
 
 RESOURCE_FILES += [
     'spacetrace.css'
diff --git a/uriloader/exthandler/tests/moz.build b/uriloader/exthandler/tests/moz.build
index 057d93da396..0f940e82341 100644
--- a/uriloader/exthandler/tests/moz.build
+++ b/uriloader/exthandler/tests/moz.build
@@ -20,10 +20,6 @@ SimplePrograms([
     'WriteArgument',
 ])
 
-SOURCES += [
-    '%s.cpp' % s for s in SIMPLE_PROGRAMS
-]
-
 USE_LIBS += [
     'nspr',
 ]
diff --git a/widget/tests/moz.build b/widget/tests/moz.build
index 31e6c40c177..ab93b2f7778 100644
--- a/widget/tests/moz.build
+++ b/widget/tests/moz.build
@@ -24,8 +24,6 @@ FAIL_ON_WARNINGS = True
 #     is bug 652123.
 #     CPP_UNIT_TESTS += ['TestChromeMargin']
 
-SOURCES += sorted('%s.cpp' % t for t in CPP_UNIT_TESTS)
-
 USE_LIBS += [
     'mozalloc',
     'nspr',
diff --git a/xpcom/reflect/xptcall/md/test/moz.build b/xpcom/reflect/xptcall/md/test/moz.build
index 65da3214d49..ebb47903c81 100644
--- a/xpcom/reflect/xptcall/md/test/moz.build
+++ b/xpcom/reflect/xptcall/md/test/moz.build
@@ -4,10 +4,6 @@
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
-SOURCES += [
-    'stub_test.cpp',
-]
-
 SimplePrograms([
     'stub_test',
 ])
diff --git a/xpcom/reflect/xptcall/tests/moz.build b/xpcom/reflect/xptcall/tests/moz.build
index 5297e3e6dd2..7bc7e8d8b9e 100644
--- a/xpcom/reflect/xptcall/tests/moz.build
+++ b/xpcom/reflect/xptcall/tests/moz.build
@@ -8,10 +8,6 @@ SimplePrograms([
     'TestXPTCInvoke',
 ])
 
-SOURCES += [
-    '%s.cpp' % s for s in SIMPLE_PROGRAMS
-]
-
 USE_LIBS += [
     'mozalloc',
     'nspr',
diff --git a/xpcom/reflect/xptinfo/tests/moz.build b/xpcom/reflect/xptinfo/tests/moz.build
index d3d3428bdcb..6022da61589 100644
--- a/xpcom/reflect/xptinfo/tests/moz.build
+++ b/xpcom/reflect/xptinfo/tests/moz.build
@@ -4,10 +4,6 @@
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
-SOURCES += [
-    'TestInterfaceInfo.cpp',
-]
-
 SimplePrograms([
     'TestInterfaceInfo'
 ])
diff --git a/xpcom/sample/program/moz.build b/xpcom/sample/program/moz.build
index 0ada27f5d2e..d00630c0475 100644
--- a/xpcom/sample/program/moz.build
+++ b/xpcom/sample/program/moz.build
@@ -4,12 +4,6 @@
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
-# We must specify CPP_SOURCES in order to link using the proper c++ linker
-# on certain platforms.
-SOURCES += [
-    'nsTestSample.cpp',
-]
-
 # SIMPLE_PROGRAMS compiles a single .cpp file into an executable
 SimplePrograms([
     'nsTestSample'
diff --git a/xpcom/tests/external/moz.build b/xpcom/tests/external/moz.build
index 5de235bb470..9999fd2c29f 100644
--- a/xpcom/tests/external/moz.build
+++ b/xpcom/tests/external/moz.build
@@ -8,10 +8,6 @@ SimplePrograms([
     'TestMinStringAPI',
 ])
 
-SOURCES += [
-    '%s.cpp' % s for s in SIMPLE_PROGRAMS
-]
-
 USE_LIBS += [
     'mozalloc',
     'nspr',
diff --git a/xpcom/tests/moz.build b/xpcom/tests/moz.build
index d677d8fd99c..320ba050987 100644
--- a/xpcom/tests/moz.build
+++ b/xpcom/tests/moz.build
@@ -48,10 +48,6 @@ if CONFIG['WRAP_STL_INCLUDES'] and not CONFIG['CLANG_CL']:
         'TestSTLWrappers',
     ])
 
-SOURCES += [
-    '%s.cpp' % s for s in sorted(SIMPLE_PROGRAMS)
-]
-
 XPCSHELL_TESTS_MANIFESTS += ['unit/xpcshell.ini']
 
 CppUnitTests([
@@ -114,8 +110,6 @@ if CONFIG['MOZ_DEBUG'] and CONFIG['OS_ARCH'] not in ('WINNT'):
         'TestDeadlockDetectorScalability',
     ])
 
-SOURCES += sorted('%s.cpp' % t for t in CPP_UNIT_TESTS)
-
 LOCAL_INCLUDES += [
     '../ds',
 ]
diff --git a/xpcom/tests/windows/moz.build b/xpcom/tests/windows/moz.build
index 5214490f2d1..0f06c8f8d1c 100644
--- a/xpcom/tests/windows/moz.build
+++ b/xpcom/tests/windows/moz.build
@@ -9,8 +9,6 @@ CppUnitTests([
     'TestNtPathToDosPath',
 ])
 
-SOURCES += sorted('%s.cpp' % t for t in CPP_UNIT_TESTS)
-
 USE_LIBS += [
     'mozalloc',
     'nspr',
diff --git a/xpcom/typelib/xpt/tests/moz.build b/xpcom/typelib/xpt/tests/moz.build
index e00c19f7b72..6fe20a8b6cf 100644
--- a/xpcom/typelib/xpt/tests/moz.build
+++ b/xpcom/typelib/xpt/tests/moz.build
@@ -9,10 +9,6 @@ SimplePrograms([
     'SimpleTypeLib',
 ])
 
-SOURCES += [
-    '%s.cpp' % s for s in SIMPLE_PROGRAMS
-]
-
 FAIL_ON_WARNINGS = True
 
 USE_LIBS += [
diff --git a/xpcom/windbgdlg/moz.build b/xpcom/windbgdlg/moz.build
index 744ecca5d9a..e5a9c0859d0 100644
--- a/xpcom/windbgdlg/moz.build
+++ b/xpcom/windbgdlg/moz.build
@@ -4,10 +4,6 @@
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
-SOURCES += [
-    'windbgdlg.cpp',
-]
-
 SimplePrograms([
     'windbgdlg'
 ])