diff --git a/Modules/GNUInstallDirs.cmake b/Modules/GNUInstallDirs.cmake
index eac553d2d..10956aac0 100644
--- a/Modules/GNUInstallDirs.cmake
+++ b/Modules/GNUInstallDirs.cmake
@@ -198,7 +198,7 @@ if(CMAKE_SYSTEM_NAME STREQUAL "OpenBSD")
     set(CMAKE_INSTALL_INFODIR "info")
   endif()
 
-  if(NOT CMAKE_INSTALL_MANDDIR)
+  if(NOT CMAKE_INSTALL_MANDIR)
     set(CMAKE_INSTALL_MANDIR "" CACHE PATH "man documentation (man)")
     set(CMAKE_INSTALL_MANDIR "man")
   endif()
@@ -208,7 +208,7 @@ else()
     set(CMAKE_INSTALL_INFODIR "${CMAKE_INSTALL_DATAROOTDIR}/info")
   endif()
 
-  if(NOT CMAKE_INSTALL_MANDDIR)
+  if(NOT CMAKE_INSTALL_MANDIR)
     set(CMAKE_INSTALL_MANDIR "" CACHE PATH "man documentation (DATAROOTDIR/man)")
     set(CMAKE_INSTALL_MANDIR "${CMAKE_INSTALL_DATAROOTDIR}/man")
   endif()