diff --git a/src/stage1/os.cpp b/src/stage1/os.cpp
index 5e5e08b083..49544102b2 100644
--- a/src/stage1/os.cpp
+++ b/src/stage1/os.cpp
@@ -42,7 +42,9 @@
 #include <fcntl.h>
 #include <ntsecapi.h>
 
-#if defined(_MSC_VER)
+// Workaround an upstream LLVM issue.
+// See https://github.com/ziglang/zig/issues/7614#issuecomment-752939981
+#if defined(_MSC_VER) && defined(_WIN64)
 typedef SSIZE_T ssize_t;
 #endif
 #else