diff --git a/libc/isystem/tgmath.h b/libc/isystem/tgmath.h
index 9b4f9728a..2f9efe946 100644
--- a/libc/isystem/tgmath.h
+++ b/libc/isystem/tgmath.h
@@ -1,6 +1,8 @@
 #ifndef LIBC_ISYSTEM_TGMATH_H_
 #define LIBC_ISYSTEM_TGMATH_H_
 
+#include "libc/math.h"
+
 #if !(__ASSEMBLER__ + __LINKER__ + 0)
 #if __STDC_VERSION__ + 0 >= 201112
 COSMOPOLITAN_C_START_