diff --git a/make/defs.mk b/make/defs.mk
index 43a2b250..cd326707 100644
--- a/make/defs.mk
+++ b/make/defs.mk
@@ -80,10 +80,23 @@ ALL_CSRC    = $(LOCAL_CSRC) $(PREREQ_CSRC)
 
 TEXTCLEAN   = $(wildcard *~ .*~ .*.swp *.rep)
 INCLUDE     = -I. -I$(TOPDIR)/include -I$(MODDIR)/include $(PROJECT_INCLUDE) $(LOCAL_INCLUDE)
+
+ifndef INSTALL_LIBDIR
 INSTALL_LIBDIR = $(PREFIX)/lib
+endif
+
+ifndef INSTALL_HDRDIR
 INSTALL_HDRDIR = $(PREFIX)/include
+endif
+
+ifndef INSTALL_MKDIR
 INSTALL_MKDIR  = $(PREFIX)/make
+endif
+
+ifndef INSTALL_BINDIR
 INSTALL_BINDIR = $(PREFIX)/bin
+endif
+
 BUILD_BINDIR   = $(TOPDIR)/bin
 INSTALL_DOCDIR_DIST = $(DOC_PREFIX)
 INSTALL_DOCDIR_DEVEL = $(DOC_PREFIX)-devel