diff --git a/xpcom/reflect/xptcall/src/md/unix/xptcstubs_x86_64_darwin.cpp b/xpcom/reflect/xptcall/src/md/unix/xptcstubs_x86_64_darwin.cpp
index 50aab3cfb18..d76e9f15b93 100644
--- a/xpcom/reflect/xptcall/src/md/unix/xptcstubs_x86_64_darwin.cpp
+++ b/xpcom/reflect/xptcall/src/md/unix/xptcstubs_x86_64_darwin.cpp
@@ -114,7 +114,7 @@ PrepareAndDispatch(nsXPTCStubBase * self, PRUint32 methodIndex,
                 // 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*) ap++;
+                dp->val.d = fpregs[nr_fpr++];
             else
                 dp->val.f = *(float*) ap++;
             continue;
diff --git a/xpcom/reflect/xptcall/src/md/unix/xptcstubs_x86_64_linux.cpp b/xpcom/reflect/xptcall/src/md/unix/xptcstubs_x86_64_linux.cpp
index 0b8013fb42b..d7f52b5d5fe 100644
--- a/xpcom/reflect/xptcall/src/md/unix/xptcstubs_x86_64_linux.cpp
+++ b/xpcom/reflect/xptcall/src/md/unix/xptcstubs_x86_64_linux.cpp
@@ -114,7 +114,7 @@ PrepareAndDispatch(nsXPTCStubBase * self, PRUint32 methodIndex,
                 // 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*) ap++;
+                dp->val.d = fpregs[nr_fpr++];
             else
                 dp->val.f = *(float*) ap++;
             continue;
diff --git a/xpcom/reflect/xptcall/src/md/unix/xptcstubs_x86_64_solaris.cpp b/xpcom/reflect/xptcall/src/md/unix/xptcstubs_x86_64_solaris.cpp
index 3ca8bd51754..af4ca423521 100644
--- a/xpcom/reflect/xptcall/src/md/unix/xptcstubs_x86_64_solaris.cpp
+++ b/xpcom/reflect/xptcall/src/md/unix/xptcstubs_x86_64_solaris.cpp
@@ -114,7 +114,7 @@ PrepareAndDispatch(nsXPTCStubBase * self, PRUint32 methodIndex,
                 // 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*) ap++;
+                dp->val.d = fpregs[nr_fpr++];
             else
                 dp->val.f = *(float*) ap++;
             continue;