diff --git a/js/src/xpconnect/tests/unit/xpcshell.ini b/js/src/xpconnect/tests/unit/xpcshell.ini
index 9433cb806cbc..64feaa3a6b52 100644
--- a/js/src/xpconnect/tests/unit/xpcshell.ini
+++ b/js/src/xpconnect/tests/unit/xpcshell.ini
@@ -22,8 +22,4 @@ fail-if = os == "android"
 [test_xpcomutils.js]
 [test_unload.js]
 [test_attributes.js]
-# Bug 689288
-fail-if = os == "win" && processor == "x86_64"
 [test_params.js]
-# Bug 689288
-fail-if = os == "win" && processor == "x86_64"
diff --git a/xpcom/reflect/xptcall/src/md/win32/xptcstubs_x86_64.cpp b/xpcom/reflect/xptcall/src/md/win32/xptcstubs_x86_64.cpp
index 3039e3f30513..bb921ca04763 100644
--- a/xpcom/reflect/xptcall/src/md/win32/xptcstubs_x86_64.cpp
+++ b/xpcom/reflect/xptcall/src/md/win32/xptcstubs_x86_64.cpp
@@ -159,7 +159,10 @@ PrepareAndDispatch(nsXPTCStubBase* self, PRUint32 methodIndex, PRUint64* args,
 
         case nsXPTType::T_FLOAT:
              if (iCount < PARAM_FPR_COUNT)
-                dp->val.f  = (float)fprData[iCount++];
+                // The value in xmm register is already prepared to
+                // be retrieved as a float. Therefore, we pass the
+                // value verbatim, as a double without conversion.
+                dp->val.d  = (double)fprData[iCount++];
              else
                 dp->val.f  = *((float*)ap++);
              break;