diff --git a/externals/Makefile b/externals/Makefile
index eb9fccf8cac77d0f35ce757a3b7e060fb6a24150..4755cb8e55a3c41423617ec741f1781b5b6f2906 100644
--- a/externals/Makefile
+++ b/externals/Makefile
@@ -533,7 +533,7 @@ freeverb_clean:
 GEM2PDP_NAME=gem2pdp
 GEM2PDP_OBJECTS := $(wildcard $(externals_src)/gem2pdp/*.cpp)
 $(externals_src)/gem2pdp/configure: $(externals_src)/gem2pdp/configure.ac
-	cd $(externals_src)/gem2pdp && autoconf
+	cd $(externals_src)/gem2pdp && aclocal && autoconf
 
 $(externals_src)/gem2pdp/Makefile: $(externals_src)/gem2pdp/Makefile.in
 	cd $(externals_src)/gem2pdp && ./configure --with-pddir=$(pd_src) \