diff --git a/gc.c b/gc.c
index ffbbee7115..cc4406c0c9 100644
--- a/gc.c
+++ b/gc.c
@@ -48,7 +48,7 @@
 # endif
 #endif
 
-#if defined(HAVE_MALLOC_USABLE_SIZE) || defined(HAVE_MALLOC_TRIM)
+#ifdef HAVE_MALLOC_USABLE_SIZE
 # ifdef RUBY_ALTERNATIVE_MALLOC_HEADER
 /* Alternative malloc header is included in ruby/missing.h */
 # elif defined(HAVE_MALLOC_H)
@@ -60,6 +60,10 @@
 # endif
 #endif
 
+#ifdef HAVE_MALLOC_TRIM
+# include <malloc.h>
+#endif
+
 #if !defined(PAGE_SIZE) && defined(HAVE_SYS_USER_H)
 /* LIST_HEAD conflicts with sys/queue.h on macOS */
 # include <sys/user.h>