diff --git a/tools/CMakeLists.txt b/tools/CMakeLists.txt
index bc0e774b5f..a8c034fb27 100644
--- a/tools/CMakeLists.txt
+++ b/tools/CMakeLists.txt
@@ -17,8 +17,16 @@
 function(configure_install_geos_config)
   string(REPLACE " " "\\ " prefix ${CMAKE_INSTALL_PREFIX})
   set(exec_prefix "$\{prefix\}")
-  set(includedir "$\{prefix\}/${CMAKE_INSTALL_INCLUDEDIR}")
-  set(libdir "$\{exec_prefix\}/${CMAKE_INSTALL_LIBDIR}")
+  if(IS_ABSOLUTE "${CMAKE_INSTALL_INCLUDEDIR}")
+    set(includedir "${CMAKE_INSTALL_INCLUDEDIR}")
+  else()
+    set(includedir "$\{prefix\}/${CMAKE_INSTALL_INCLUDEDIR}")
+  endif()
+  if(IS_ABSOLUTE "${CMAKE_INSTALL_LIBDIR}")
+    set(libdir "${CMAKE_INSTALL_LIBDIR}")
+  else()
+    set(libdir "$\{exec_prefix\}/${CMAKE_INSTALL_LIBDIR}")
+  endif()
   set(VERSION_RELEASE ${GEOS_VERSION_MAJOR})
   set(VERSION ${GEOS_VERSION})
 
@@ -42,8 +50,16 @@ endfunction()
 function(configure_install_geos_pc)
   string(REPLACE " " "\\ " prefix ${CMAKE_INSTALL_PREFIX})
   set(exec_prefix "$\{prefix\}")
-  set(includedir "$\{prefix\}/${CMAKE_INSTALL_INCLUDEDIR}")
-  set(libdir "$\{exec_prefix\}/${CMAKE_INSTALL_LIBDIR}")
+  if(IS_ABSOLUTE "${CMAKE_INSTALL_INCLUDEDIR}")
+    set(includedir "${CMAKE_INSTALL_INCLUDEDIR}")
+  else()
+    set(includedir "$\{prefix\}/${CMAKE_INSTALL_INCLUDEDIR}")
+  endif()
+  if(IS_ABSOLUTE "${CMAKE_INSTALL_LIBDIR}")
+    set(libdir "${CMAKE_INSTALL_LIBDIR}")
+  else()
+    set(libdir "$\{exec_prefix\}/${CMAKE_INSTALL_LIBDIR}")
+  endif()
   set(VERSION ${GEOS_VERSION})
   set(EXTRA_LIBS "-lstdc++")
   if(HAVE_LIBM)