diff --git a/src/racket/configure.ac b/src/racket/configure.ac
index 5db772dedb..5384a13e82 100644
--- a/src/racket/configure.ac
+++ b/src/racket/configure.ac
@@ -560,6 +560,7 @@ case $OS in
   FreeBSD)
     LIBS="$LIBS -rdynamic"
     DYN_CFLAGS="-fPIC"
+    GC_THREADS_FLAG="-DGC_FREEBSD_THREADS"
     enable_pthread=yes
     ;;
   OpenBSD)
diff --git a/src/racket/src/mzrt.h b/src/racket/src/mzrt.h
index 3d07fe5bad..4a0d1d8ca3 100644
--- a/src/racket/src/mzrt.h
+++ b/src/racket/src/mzrt.h
@@ -27,6 +27,7 @@ void mzrt_set_user_break_handler(void (*user_break_handler)(int));
 # include <winsock2.h>
 typedef HANDLE mzrt_thread_id;
 #else
+#include <pthread.h>
 typedef pthread_t mzrt_thread_id;
 #endif