diff --git a/CMakeLists.txt b/CMakeLists.txt
index 2fb555a9..5af4362f 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -195,11 +195,6 @@ if (UNIX)
         check_include_files ("X11/extensions/XInput2.h" HAVE_XI2)
         check_include_files ("dns_sd.h" HAVE_DNSSD)
 
-        if (HAVE_X11_EXTENSIONS_DPMS_H)
-            # Assume that function prototypes declared, when include exists.
-            set (HAVE_DPMS_PROTOTYPES 1)
-        endif()
-
         if (NOT HAVE_X11_EXTENSIONS_XTEST_H)
             message (FATAL_ERROR "Missing header: X11/extensions/XTest.h")
         endif()
diff --git a/res/config.h.in b/res/config.h.in
index eb1e34fb..a2216875 100644
--- a/res/config.h.in
+++ b/res/config.h.in
@@ -19,9 +19,6 @@
 /* Define if your compiler has standard C++ library support. */
 #cmakedefine HAVE_CXX_STDLIB ${HAVE_CXX_STDLIB}
 
-/* Define if the <X11/extensions/dpms.h> header file declares function prototypes. */
-#cmakedefine HAVE_DPMS_PROTOTYPES ${HAVE_DPMS_PROTOTYPES}
-
 /* Define if you have a working `getpwuid_r` function. */
 #cmakedefine HAVE_GETPWUID_R ${HAVE_GETPWUID_R}
 
diff --git a/src/lib/platform/XWindowsScreenSaver.cpp b/src/lib/platform/XWindowsScreenSaver.cpp
index a02fdfd5..be1d7d43 100644
--- a/src/lib/platform/XWindowsScreenSaver.cpp
+++ b/src/lib/platform/XWindowsScreenSaver.cpp
@@ -31,22 +31,6 @@
 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