diff --git a/crypto/mem.c b/crypto/mem.c
index ca4c559..f44e90f 100644
--- a/crypto/mem.c
+++ b/crypto/mem.c
@@ -69,6 +69,14 @@
 OPENSSL_MSVC_PRAGMA(warning(push, 3))
 #include <windows.h>
 OPENSSL_MSVC_PRAGMA(warning(pop))
+
+/* Work around a clang-cl bug: SecureZeroMemory() below uses __stosb() but
+ * windows.h only declares that intrinsic and then uses `#pragma intrinsic` for
+ * it.  clang-cl doesn't implement `#pragma intrinsic` yet; it instead defines
+ * the function as an always-inline symbol in its intrin.h.
+ * TODO(thakis): Remove this once http://llvm.org/PR19898 is fixed.
+ */
+#include <intrin.h>
 #else
 #include <strings.h>
 #endif