diff --git a/media/libspeex_resampler/src/moz.build b/media/libspeex_resampler/src/moz.build
index d7d0d73b272..631926c36f1 100644
--- a/media/libspeex_resampler/src/moz.build
+++ b/media/libspeex_resampler/src/moz.build
@@ -39,5 +39,9 @@ else:
 if CONFIG['INTEL_ARCHITECTURE'] and CONFIG['OS_TARGET'] != 'Android':
     DEFINES['_USE_SSE'] = True
     DEFINES['_USE_SSE2'] = True
+
+# Suppress warnings in third-party code.
+if CONFIG['OS_TARGET'] == 'Darwin':
+    CFLAGS += ['-Wno-sign-compare']
     if CONFIG['GNU_CC']:
         SOURCES['resample.c'].flags += ['-msse2']
diff --git a/media/libtheora/lib/moz.build b/media/libtheora/lib/moz.build
index fbf96091609..d46f7b2d6f0 100644
--- a/media/libtheora/lib/moz.build
+++ b/media/libtheora/lib/moz.build
@@ -76,3 +76,7 @@ FINAL_LIBRARY = 'gkmedias'
 
 # The encoder is currently not included.
 DEFINES['THEORA_DISABLE_ENCODE'] = True
+
+# Suppress warnings in third-party code.
+if CONFIG['OS_TARGET'] == 'Darwin':
+    CFLAGS += ['-Wno-tautological-compare']
diff --git a/media/libvpx/moz.build b/media/libvpx/moz.build
index a2fcee782f9..54978241803 100644
--- a/media/libvpx/moz.build
+++ b/media/libvpx/moz.build
@@ -87,6 +87,8 @@ if CONFIG['OS_TARGET'] == 'Android':
         SOURCES += [
             '%s/sources/android/cpufeatures/cpu-features.c' % CONFIG['ANDROID_NDK'],
         ]
+elif CONFIG['OS_TARGET'] == 'Darwin':
+    CFLAGS += ['-Wno-sign-compare']
 
 if not CONFIG['_MSC_VER']:
     for f in SOURCES: