diff --git a/cmake/Libraries.cmake b/cmake/Libraries.cmake
index 2698f4ef3..062d184b4 100644
--- a/cmake/Libraries.cmake
+++ b/cmake/Libraries.cmake
@@ -194,11 +194,6 @@ macro(configure_xorg_libs)
   check_include_files("${XKBlib}" HAVE_X11_XKBLIB_H)
   check_include_files("X11/extensions/XInput2.h" HAVE_XI2)
 
-  if(HAVE_X11_EXTENSIONS_DPMS_H)
-    # Assume that function prototypes declared, when include exists.
-    set(HAVE_DPMS_PROTOTYPES 1)
-  endif()
-
   if(NOT HAVE_X11_XKBLIB_H)
     message(FATAL_ERROR "Missing header: " ${XKBlib})
   endif()
diff --git a/src/lib/Config.h.in b/src/lib/Config.h.in
index 83cff869c..e3f63d2e0 100644
--- a/src/lib/Config.h.in
+++ b/src/lib/Config.h.in
@@ -7,9 +7,6 @@
 
 // clang-format off
 
-/* Define if the <X11/extensions/dpms.h> header file declares function prototypes. */
-#cmakedefine HAVE_DPMS_PROTOTYPES @HAVE_DPMS_PROTOTYPES@
-
 /* Define if you have the `inet_aton` function. */
 #cmakedefine HAVE_INET_ATON @HAVE_INET_ATON@
 
diff --git a/src/lib/platform/XWindowsScreenSaver.cpp b/src/lib/platform/XWindowsScreenSaver.cpp
index bbcd90cdd..0d1c5f314 100644
--- a/src/lib/platform/XWindowsScreenSaver.cpp
+++ b/src/lib/platform/XWindowsScreenSaver.cpp
@@ -25,22 +25,6 @@ extern "C"
 {
 #include <X11/Xmd.h>
 #include <X11/extensions/dpms.h>
-#if !HAVE_DPMS_PROTOTYPES
-#undef DPMSModeOn
-#undef DPMSModeStandby
-#undef DPMSModeSuspend
-#undef DPMSModeOff
-#define DPMSModeOn 0
-#define DPMSModeStandby 1
-#define DPMSModeSuspend 2
-#define DPMSModeOff 3
-  extern Bool DPMSQueryExtension(Display *, int *, int *);
-  extern Bool DPMSCapable(Display *);
-  extern Status DPMSEnable(Display *);
-  extern Status DPMSDisable(Display *);
-  extern Status DPMSForceLevel(Display *, CARD16);
-  extern Status DPMSInfo(Display *, CARD16 *, BOOL *);
-#endif
 }
 #endif