diff --git a/lib/std/c/dragonfly.zig b/lib/std/c/dragonfly.zig
index 6782aa098a..268391c830 100644
--- a/lib/std/c/dragonfly.zig
+++ b/lib/std/c/dragonfly.zig
@@ -21,7 +21,6 @@ pub extern "c" fn dl_iterate_phdr(callback: dl_iterate_phdr_callback, data: ?*an
 pub extern "c" fn lwp_gettid() c_int;
 
 pub extern "c" fn posix_memalign(memptr: *?*anyopaque, alignment: usize, size: usize) c_int;
-pub extern "c" fn malloc_usable_size(?*const anyopaque) usize;
 
 pub const pthread_mutex_t = extern struct {
     inner: ?*anyopaque = null,
diff --git a/lib/std/c/haiku.zig b/lib/std/c/haiku.zig
index c47ceeb003..7aba395b75 100644
--- a/lib/std/c/haiku.zig
+++ b/lib/std/c/haiku.zig
@@ -1071,5 +1071,3 @@ pub const sigevent = extern struct {
 
 /// TODO refines if necessary
 pub const PTHREAD_STACK_MIN = 2 * 4096;
-
-pub extern "c" fn malloc_usable_size(?*anyopaque) usize;