diff --git a/build/autotools/configure.ac b/build/autotools/configure.ac
index 53c34d2e535..3830a25b0b2 100644
--- a/build/autotools/configure.ac
+++ b/build/autotools/configure.ac
@@ -111,7 +111,7 @@ AS_CASE([$host_os],
   LIBOPENMPT_LIBS_PRIVATE_WIN32=
   LIBOPENMPTTEST_WIN32_LIBS="-lole32 -lrpcrt4"
   OPENMPT123_WIN32_LIBS=-lwinmm
-  WIN32_CPPFLAGS="-DNOMINMAX"
+  WIN32_CPPFLAGS="-D_UNICODE -DNOMINMAX"
   WIN32_CXXFLAGS="-municode -mthreads"
   WIN32_CFLAGS="-municode -mthreads"
   WIN32_CONSOLE_CXXFLAGS=-mconsole