diff --git a/lib/std/os.zig b/lib/std/os.zig
index f170eec367..cb988ca9a8 100644
--- a/lib/std/os.zig
+++ b/lib/std/os.zig
@@ -5620,7 +5620,7 @@ pub fn sigaction(sig: u6, noalias act: ?*const Sigaction, noalias oact: ?*Sigact
 
 /// Sets the thread signal mask.
 pub fn sigprocmask(flags: u32, noalias set: ?*const sigset_t, noalias oldset: ?*sigset_t) void {
-    switch (errno(system.sigprocmask(flags, set, oldset))) {
+    switch (errno(system.sigprocmask(@bitCast(flags), set, oldset))) {
         .SUCCESS => return,
         .FAULT => unreachable,
         .INVAL => unreachable,