diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 90f0bcb4..68efcc53 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -221,10 +221,20 @@ else()
   set(LIBSSH2_PC_REQUIRES "${LIBSSH2_PC_REQUIRES_PRIVATE}")
   set(LIBSSH2_PC_LIBS "${LIBSSH2_PC_LIBS_PRIVATE}")
 endif()
-set(prefix ${CMAKE_INSTALL_PREFIX})
-set(exec_prefix "\${prefix}")
-set(libdir "\${prefix}/${CMAKE_INSTALL_LIBDIR}")
-set(includedir "\${prefix}/${CMAKE_INSTALL_INCLUDEDIR}")
+
+set(prefix       "${CMAKE_INSTALL_PREFIX}")
+set(exec_prefix  "\${prefix}")
+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}/${CMAKE_INSTALL_LIBDIR}")
+endif()
+
 configure_file("${PROJECT_SOURCE_DIR}/libssh2.pc.in" "libssh2.pc" @ONLY)
 install(
   FILES "${CMAKE_CURRENT_BINARY_DIR}/libssh2.pc"