diff --git a/Source/Makefile.in b/Source/Makefile.in
index a9786c971..3aec7c941 100644
--- a/Source/Makefile.in
+++ b/Source/Makefile.in
@@ -49,7 +49,7 @@ LEX = flex
 LEXFLAGS =
 YACC = bison
 
-DEFS = @DEFS@
+DEFS = -DGNUSTEP_INSTALL_PREFIX=$(prefix) @DEFS@
 
 # File name extensions
 OEXT = .o