--- a/old-configure.in
+++ b/old-configure.in
@@ -1083,16 +1083,20 @@ case "$target" in
             if test -z `echo $CXXFLAGS | grep -i [-/]arch:`; then
               CXXFLAGS="$CXXFLAGS -arch:SSE2"
             fi
             SSE_FLAGS="-arch:SSE"
             SSE2_FLAGS="-arch:SSE2"
             dnl MSVC allows the use of intrinsics without any flags
             dnl and doesn't have a separate arch for SSSE3
             SSSE3_FLAGS="-arch:SSE2"
+            dnl clang-cl, however, requires the appropriate flags.
+            if test -n "$CLANG_CL"; then
+                SSSE3_FLAGS="-mssse3"
+            fi
         fi
         dnl VS2013+ requires -FS when parallel building by make -jN.
         dnl If nothing, compiler sometimes causes C1041 error.
         CFLAGS="$CFLAGS -FS"
         CXXFLAGS="$CXXFLAGS -FS"
         # khuey says we can safely ignore MSVC warning C4251
         # MSVC warning C4244 (implicit type conversion may lose data) warns
         # and requires workarounds for perfectly valid code.  Also, GCC/clang