diff --git a/js/src/jsanalyze.cpp b/js/src/jsanalyze.cpp
index ac703fd9ebd..41a8509f260 100644
--- a/js/src/jsanalyze.cpp
+++ b/js/src/jsanalyze.cpp
@@ -1894,6 +1894,12 @@ SSAValue::print() const
     }
 }
 
+void
+ScriptAnalysis::assertMatchingDebugMode()
+{
+    JS_ASSERT(!!script->compartment()->debugMode() == !!originalDebugMode_);
+}
+
 #endif  /* DEBUG */
 
 } /* namespace analyze */
diff --git a/js/src/jsanalyze.h b/js/src/jsanalyze.h
index e4e5d2921a2..38ca6a8cf8b 100644
--- a/js/src/jsanalyze.h
+++ b/js/src/jsanalyze.h
@@ -822,6 +822,11 @@ class ScriptAnalysis
     bool ranLifetimes_;
     bool ranInference_;
 
+#ifdef DEBUG
+    /* Whether the compartment was in debug mode when we performed the analysis. */
+    bool originalDebugMode_: 1;
+#endif
+
     /* --------- Bytecode analysis --------- */
 
     bool usesReturnValue_:1;
@@ -843,7 +848,13 @@ class ScriptAnalysis
 
   public:
 
-    ScriptAnalysis(JSScript *script) { PodZero(this); this->script = script; }
+    ScriptAnalysis(JSScript *script) { 
+        PodZero(this);
+        this->script = script;
+#ifdef DEBUG
+        this->originalDebugMode_ = script->compartment()->debugMode();
+#endif        
+    }
 
     bool ranBytecode() { return ranBytecode_; }
     bool ranSSA() { return ranSSA_; }
@@ -1164,6 +1175,13 @@ class ScriptAnalysis
     bool analyzeTypesBytecode(JSContext *cx, unsigned offset, TypeInferenceState &state);
     bool followEscapingArguments(JSContext *cx, const SSAValue &v, Vector<SSAValue> *seen);
     bool followEscapingArguments(JSContext *cx, SSAUseChain *use, Vector<SSAValue> *seen);
+
+  public:
+#ifdef DEBUG
+    void assertMatchingDebugMode();
+#else
+    void assertMatchingDebugMode() { }
+#endif
 };
 
 /* Protect analysis structures from GC while they are being used. */
diff --git a/js/src/jscompartment.cpp b/js/src/jscompartment.cpp
index ad862a7ccc2..5e611e54cb7 100644
--- a/js/src/jscompartment.cpp
+++ b/js/src/jscompartment.cpp
@@ -639,13 +639,14 @@ JSCompartment::updateForDebugMode(JSContext *cx)
     }
 
     /*
-     * Discard JIT code for any scripts that change debugMode. This assumes
-     * that 'comp' is in the same thread as 'cx'.
+     * Discard JIT code and bytecode analyses for any scripts that change
+     * debugMode. This assumes that 'comp' is in the same thread as 'cx'.
      */
     for (gc::CellIter i(cx, this, gc::FINALIZE_SCRIPT); !i.done(); i.next()) {
         JSScript *script = i.get<JSScript>();
         if (script->debugMode != enabled) {
             mjit::ReleaseScriptCode(cx, script);
+            script->clearAnalysis();
             script->debugMode = enabled;
         }
     }
diff --git a/js/src/methodjit/Compiler.cpp b/js/src/methodjit/Compiler.cpp
index d788afdc87a..2c3d452fafc 100644
--- a/js/src/methodjit/Compiler.cpp
+++ b/js/src/methodjit/Compiler.cpp
@@ -189,6 +189,7 @@ mjit::Compiler::checkAnalysis(JSScript *script)
         return Compile_Error;
 
     ScriptAnalysis *analysis = script->analysis();
+    analysis->assertMatchingDebugMode();
     if (analysis->failed()) {
         JaegerSpew(JSpew_Abort, "couldn't analyze bytecode; probably switchX or OOM\n");
         return Compile_Abort;