new file mode 100644
--- /dev/null
+++ b/js/src/jit-test/tests/wasm/regress/nop-fill-jit-exit.js
@@ -0,0 +1,28 @@
+// |jit-test| --arm-asm-nop-fill=1
+//
+try {
+    enableSingleStepProfiling();
+    disableSingleStepProfiling();
+} catch (e) {
+    // Early quit on plateforms not supporting single step profiling.
+    quit();
+}
+
+load(libdir + "asm.js");
+
+var ffi = function(enable) {
+    enableGeckoProfiling();
+    enableSingleStepProfiling();
+}
+var f = asmLink(asmCompile('global', 'ffis',
+  USE_ASM + `
+    var ffi=ffis.ffi;
+    function f(i) {
+      i=i|0;
+      ffi(i|0);
+    } return f
+  `), null, {
+    ffi
+});
+f(0);
+f(+1);

--- a/js/src/wasm/WasmTypes.cpp
+++ b/js/src/wasm/WasmTypes.cpp
@@ -754,16 +754,18 @@ CodeRange::CodeRange(uint32_t funcIndex,
     kind_(ImportJitExit)
 {
     MOZ_ASSERT(isImportJitExit());
     MOZ_ASSERT(begin_ < ret_);
     MOZ_ASSERT(ret_ < end_);
     u.funcIndex_ = funcIndex;
     u.jitExit.beginToUntrustedFPStart_ = offsets.untrustedFPStart - begin_;
     u.jitExit.beginToUntrustedFPEnd_ = offsets.untrustedFPEnd - begin_;
+    MOZ_ASSERT(jitExitUntrustedFPStart() == offsets.untrustedFPStart);
+    MOZ_ASSERT(jitExitUntrustedFPEnd() == offsets.untrustedFPEnd);
 }
 
 CodeRange::CodeRange(Trap trap, CallableOffsets offsets)
   : begin_(offsets.begin),
     ret_(offsets.ret),
     end_(offsets.end),
     kind_(TrapExit)
 {

--- a/js/src/wasm/WasmTypes.h
+++ b/js/src/wasm/WasmTypes.h
@@ -1016,18 +1016,18 @@ class CodeRange
             uint32_t funcIndex_;
             union {
                 struct {
                     uint32_t lineOrBytecode_;
                     uint8_t beginToNormalEntry_;
                     uint8_t beginToTierEntry_;
                 } func;
                 struct {
-                    uint8_t beginToUntrustedFPStart_;
-                    uint8_t beginToUntrustedFPEnd_;
+                    uint16_t beginToUntrustedFPStart_;
+                    uint16_t beginToUntrustedFPEnd_;
                 } jitExit;
             };
         };
         Trap trap_;
     } u;
     Kind kind_ : 8;
 
   public: