diff --git a/make/defs.mk b/make/defs.mk
index 5ef7b3f9..a6181ee1 100644
--- a/make/defs.mk
+++ b/make/defs.mk
@@ -1369,6 +1369,9 @@ LIBFLAGS                  += -L$(SCOPE_CASMIX_DIR)/lib -lscope-casmix
 EXE_SEARCH_PATH           += $(SCOPE_CASMIX_DIR)/bin
 endif
 
+PREREQ_INSTALL            ?= $(PREREQ_BUILD)
+PREREQ_RUN                ?= $(PREREQ_INSTALL)
+
 ifeq ($(USE_SNDFILE),true)
 LIBFLAGS                  += -lsndfile
 endif