diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_internal_defs.h b/compiler-rt/lib/sanitizer_common/sanitizer_internal_defs.h
index 3af47c2e2ff7a..1607436e476e5 100644
--- a/compiler-rt/lib/sanitizer_common/sanitizer_internal_defs.h
+++ b/compiler-rt/lib/sanitizer_common/sanitizer_internal_defs.h
@@ -194,7 +194,16 @@ typedef u64  OFF64_T;
 #ifdef __SIZE_TYPE__
 typedef __SIZE_TYPE__ usize;
 #else
+// Since we use this for operator new, usize must match the real size_t, but on
+// 32-bit Windows the definition of uptr does not actually match uintptr_t or
+// size_t because we are working around typedef mismatches for the (S)SIZE_T
+// types used in interception.h.
+// Until the definition of uptr has been fixed we have to special case Win32.
+#  if SANITIZER_WINDOWS && SANITIZER_WORDSIZE == 32
+typedef unsigned int usize;
+#  else
 typedef uptr usize;
+#  endif
 #endif
 
 typedef u64 tid_t;