diff --git a/js/src/jit-test/tests/basic/bug657975.js b/js/src/jit-test/tests/basic/bug657975.js
index 659aab5b38d..c734b39be56 100644
--- a/js/src/jit-test/tests/basic/bug657975.js
+++ b/js/src/jit-test/tests/basic/bug657975.js
@@ -37,3 +37,10 @@ function f6() {
 }
 trap(f6, 10, '')
 f6()
+
+// bug 658491
+function f7() {
+  try { y = w; } catch(y) {}
+}
+trap(f7, 16, '')
+f7()
diff --git a/js/src/methodjit/Compiler.cpp b/js/src/methodjit/Compiler.cpp
index ea2b906346c..1710fb2f024 100644
--- a/js/src/methodjit/Compiler.cpp
+++ b/js/src/methodjit/Compiler.cpp
@@ -1510,6 +1510,17 @@ mjit::Compiler::generateMethod()
         SPEW_OPCODE();
         JS_ASSERT(frame.stackDepth() == opinfo->stackDepth);
 
+        // If this is an exception entry point, then jsl_InternalThrow has set
+        // VMFrame::fp to the correct fp for the entry point. We need to copy
+        // that value here to FpReg so that FpReg also has the correct sp.
+        // Otherwise, we would simply be using a stale FpReg value.
+        // Additionally, we check the interrupt flag to allow interrupting
+        // deeply nested exception handling.
+        if (op == JSOP_ENTERBLOCK && analysis->getCode(PC).exceptionEntry) {
+            masm.loadPtr(FrameAddress(VMFrame::offsetOfFp), JSFrameReg);
+            interruptCheckHelper();
+        }
+
         if (trap) {
             prepareStubCall(Uses(0));
             masm.move(Imm32(trap), Registers::ArgReg1);
@@ -6661,17 +6672,6 @@ mjit::Compiler::jumpAndTrace(Jump j, jsbytecode *target, Jump *slow, bool *tramp
 void
 mjit::Compiler::enterBlock(JSObject *obj)
 {
-    // If this is an exception entry point, then jsl_InternalThrow has set
-    // VMFrame::fp to the correct fp for the entry point. We need to copy
-    // that value here to FpReg so that FpReg also has the correct sp.
-    // Otherwise, we would simply be using a stale FpReg value.
-    // Additionally, we check the interrupt flag to allow interrupting
-    // deeply nested exception handling.
-    if (analysis->getCode(PC).exceptionEntry) {
-        masm.loadPtr(FrameAddress(VMFrame::offsetOfFp), JSFrameReg);
-        interruptCheckHelper();
-    }
-
     /* For now, don't bother doing anything for this opcode. */
     frame.syncAndForgetEverything();
     masm.move(ImmPtr(obj), Registers::ArgReg1);