diff --git a/js/src/asmjs/WasmInstance.cpp b/js/src/asmjs/WasmInstance.cpp
index 3a5964ab2fb6..7f303723037a 100644
--- a/js/src/asmjs/WasmInstance.cpp
+++ b/js/src/asmjs/WasmInstance.cpp
@@ -505,8 +505,8 @@ Instance::memoryLength() const
 }
 
 template<typename T>
-static JSObject*
-CreateCustomNaNObject(JSContext* cx, T* addr)
+JSObject*
+js::wasm::CreateCustomNaNObject(JSContext* cx, T* addr)
 {
     MOZ_ASSERT(IsNaN(*addr));
 
@@ -528,8 +528,11 @@ CreateCustomNaNObject(JSContext* cx, T* addr)
     return obj;
 }
 
-static bool
-ReadCustomFloat32NaNObject(JSContext* cx, HandleValue v, uint32_t* ret)
+template JSObject* js::wasm::CreateCustomNaNObject(JSContext* cx, float* addr);
+template JSObject* js::wasm::CreateCustomNaNObject(JSContext* cx, double* addr);
+
+bool
+js::wasm::ReadCustomFloat32NaNObject(JSContext* cx, HandleValue v, uint32_t* ret)
 {
     RootedObject obj(cx, &v.toObject());
     RootedValue val(cx);
@@ -544,8 +547,8 @@ ReadCustomFloat32NaNObject(JSContext* cx, HandleValue v, uint32_t* ret)
     return true;
 }
 
-static bool
-ReadCustomDoubleNaNObject(JSContext* cx, HandleValue v, uint64_t* ret)
+bool
+js::wasm::ReadCustomDoubleNaNObject(JSContext* cx, HandleValue v, uint64_t* ret)
 {
     RootedObject obj(cx, &v.toObject());
     RootedValue val(cx);
diff --git a/js/src/asmjs/WasmInstance.h b/js/src/asmjs/WasmInstance.h
index c2c0d1401076..bb3102ee08ae 100644
--- a/js/src/asmjs/WasmInstance.h
+++ b/js/src/asmjs/WasmInstance.h
@@ -139,6 +139,25 @@ class Instance
 
 typedef UniquePtr<Instance> UniqueInstance;
 
+// Converts a testing-only NaN JS object with a nan_low field to a float32 NaN
+// with nan_low as the payload.
+
+bool
+ReadCustomFloat32NaNObject(JSContext* cx, HandleValue v, uint32_t* ret);
+
+// Converts a testing-only NaN JS object with nan_{low,high} components to a
+// double NaN with nan_low|(nan_high)>>32 as the payload.
+
+bool
+ReadCustomDoubleNaNObject(JSContext* cx, HandleValue v, uint64_t* ret);
+
+// Creates a testing-only NaN JS object with fields as described above, for
+// T=float or T=double.
+
+template<typename T>
+JSObject*
+CreateCustomNaNObject(JSContext* cx, T* addr);
+
 } // namespace wasm
 } // namespace js
 
diff --git a/js/src/asmjs/WasmIonCompile.cpp b/js/src/asmjs/WasmIonCompile.cpp
index 68f441888a52..f06b6ce3bcc3 100644
--- a/js/src/asmjs/WasmIonCompile.cpp
+++ b/js/src/asmjs/WasmIonCompile.cpp
@@ -2027,10 +2027,10 @@ EmitGetGlobal(FunctionCompiler& f)
         result = f.constant(int64_t(value.i64()));
         break;
       case ValType::F32:
-        result = f.constant(Float32Value(value.f32().fp()), mirType);
+        result = f.constant(value.f32());
         break;
       case ValType::F64:
-        result = f.constant(DoubleValue(value.f64().fp()), mirType);
+        result = f.constant(value.f64());
         break;
       case ValType::I8x16:
         result = f.constant(SimdConstant::CreateX16(value.i8x16()), mirType);
diff --git a/js/src/asmjs/WasmJS.cpp b/js/src/asmjs/WasmJS.cpp
index 15d3c77456ff..f5e2ae8ba8c7 100644
--- a/js/src/asmjs/WasmJS.cpp
+++ b/js/src/asmjs/WasmJS.cpp
@@ -161,6 +161,13 @@ GetImports(JSContext* cx,
                 break;
               }
               case ValType::F32: {
+                if (JitOptions.wasmTestMode && v.isObject()) {
+                    uint32_t bits;
+                    if (!ReadCustomFloat32NaNObject(cx, v, &bits))
+                        return false;
+                    val = Val(RawF32::fromBits(bits));
+                    break;
+                }
                 double d;
                 if (!ToNumber(cx, v, &d))
                     return false;
@@ -168,6 +175,13 @@ GetImports(JSContext* cx,
                 break;
               }
               case ValType::F64: {
+                if (JitOptions.wasmTestMode && v.isObject()) {
+                    uint64_t bits;
+                    if (!ReadCustomDoubleNaNObject(cx, v, &bits))
+                        return false;
+                    val = Val(RawF64::fromBits(bits));
+                    break;
+                }
                 double d;
                 if (!ToNumber(cx, v, &d))
                     return false;
diff --git a/js/src/asmjs/WasmModule.cpp b/js/src/asmjs/WasmModule.cpp
index f920862c4876..7158a65a811a 100644
--- a/js/src/asmjs/WasmModule.cpp
+++ b/js/src/asmjs/WasmModule.cpp
@@ -714,11 +714,29 @@ GetGlobalExport(JSContext* cx, const GlobalDescVector& globals, uint32_t globalI
         return true;
       }
       case ValType::F32: {
-        jsval.set(DoubleValue(double(val.f32().fp())));
+        float f = val.f32().fp();
+        if (JitOptions.wasmTestMode && IsNaN(f)) {
+            uint32_t bits = val.f32().bits();
+            RootedObject obj(cx, CreateCustomNaNObject(cx, (float*)&bits));
+            if (!obj)
+                return false;
+            jsval.set(ObjectValue(*obj));
+            return true;
+        }
+        jsval.set(DoubleValue(double(f)));
         return true;
       }
       case ValType::F64: {
-        jsval.set(DoubleValue(val.f64().fp()));
+        double d = val.f64().fp();
+        if (JitOptions.wasmTestMode && IsNaN(d)) {
+            uint64_t bits = val.f64().bits();
+            RootedObject obj(cx, CreateCustomNaNObject(cx, (double*)&bits));
+            if (!obj)
+                return false;
+            jsval.set(ObjectValue(*obj));
+            return true;
+        }
+        jsval.set(DoubleValue(d));
         return true;
       }
       default: {