diff --git a/libc/spec/gnu_ext.td b/libc/spec/gnu_ext.td
new file mode 100644
--- /dev/null
+++ b/libc/spec/gnu_ext.td
@@ -0,0 +1,19 @@
+def GnuExtensions : StandardSpec<"GNUExtensions"> {
+  HeaderSpec Math = HeaderSpec<
+      "math.h",
+      [], // Macros
+      [], // Types
+      [], // Enumerations
+      [
+        FunctionSpec<
+            "sincosf",
+            RetValSpec<VoidType>,
+            [ArgSpec<FloatType>, ArgSpec<FloatPtr>, ArgSpec<FloatPtr>]
+        >,
+      ]
+  >;
+
+  let Headers = [
+    Math,
+  ];
+}
diff --git a/libc/spec/spec.td b/libc/spec/spec.td
--- a/libc/spec/spec.td
+++ b/libc/spec/spec.td
@@ -47,6 +47,7 @@
 // Common types
 def VoidPtr : PtrType<VoidType>;
 def SizeTType : NamedType<"size_t">;
+def FloatPtr : PtrType<FloatType>;
 
 // _Noreturn is really not a type, but it is convenient to treat it as a type.
 def NoReturn : NamedType<"_Noreturn void">;