diff --git a/src/lib/config.h.in b/src/lib/config.h.in
index aae31281a..d4abb36bc 100644
--- a/src/lib/config.h.in
+++ b/src/lib/config.h.in
@@ -181,7 +181,4 @@
 /* Define to 1 if the X Window System is missing or not being used. */
 #cmakedefine X_DISPLAY_MISSING @X_DISPLAY_MISSING@
 
-/* Define to `unsigned int` if <sys/types.h> does not define. */
-#cmakedefine size_t @size_t@
-
 // clang-format on