diff --git a/rttopo.pc.in b/rttopo.pc.in
index 86c71dc..4064506 100644
--- a/rttopo.pc.in
+++ b/rttopo.pc.in
@@ -10,3 +10,4 @@ Description: the RT Topology library
 Version: @VERSION@
 Libs: -L${libdir} -lrttopo -lm
 Cflags: -I${includedir} 
+Requires.private: geos