diff --git a/gfx/angle/README.mozilla b/gfx/angle/README.mozilla
index 181013e25b4b9..e44cb5085090c 100644
--- a/gfx/angle/README.mozilla
+++ b/gfx/angle/README.mozilla
@@ -7,6 +7,8 @@ Local patches:
 
     angle-fixes.patch - fix angle issues 51 & 52
 
+    angle-nspr-misc.patch - don't bother with ANGLE_OS detection with NSPR
+
 == Visual Studio Solution Files ==
 
 The VS solution/project files that are used to build ANGLE are built
diff --git a/gfx/angle/angle-nspr-misc.patch b/gfx/angle/angle-nspr-misc.patch
new file mode 100644
index 0000000000000..b936ccd0448d4
--- /dev/null
+++ b/gfx/angle/angle-nspr-misc.patch
@@ -0,0 +1,17 @@
+# HG changeset patch
+# Parent f0e6e4c311dd940147f1589d72cc87f8ce755697
+diff --git a/gfx/angle/src/compiler/osinclude.h b/gfx/angle/src/compiler/osinclude.h
+--- a/gfx/angle/src/compiler/osinclude.h
++++ b/gfx/angle/src/compiler/osinclude.h
+@@ -12,8 +12,10 @@
+ // declares any os-specific functions.
+ //
+ 
+-#if defined(_WIN32) || defined(_WIN64)
++#if defined(ANGLE_USE_NSPR)
++/* no need to define anything when using NSPR */
++#elif defined(_WIN32) || defined(_WIN64)
+ #define ANGLE_OS_WIN
+ #elif defined(__APPLE__) || defined(__linux__) || \
+       defined(__FreeBSD__) || defined(__OpenBSD__) || \
+       defined(__sun)
diff --git a/gfx/angle/src/compiler/osinclude.h b/gfx/angle/src/compiler/osinclude.h
index 1af5064b09a81..d71b3c2d46be2 100644
--- a/gfx/angle/src/compiler/osinclude.h
+++ b/gfx/angle/src/compiler/osinclude.h
@@ -12,7 +12,9 @@
 // declares any os-specific functions.
 //
 
-#if defined(_WIN32) || defined(_WIN64)
+#if defined(ANGLE_USE_NSPR)
+/* no need to define anything when using NSPR */
+#elif defined(_WIN32) || defined(_WIN64)
 #define ANGLE_OS_WIN
 #elif defined(__APPLE__) || defined(__linux__) || \
       defined(__FreeBSD__) || defined(__OpenBSD__) || \