diff --git a/config.h.cmake b/config.h.cmake
index 3bed93bc..df1f6404 100644
--- a/config.h.cmake
+++ b/config.h.cmake
@@ -52,6 +52,9 @@
 #cmakedefine HAVE_UTMP_H 1
 #cmakedefine HAVE_UTMPX_H 1
 #cmakedefine HAVE_VSNPRINTF 1
+#cmakedefine HAVE_STRERROR 1
+#cmakedefine HAVE_STRERROR_PROTO 1
+#cmakedefine HAVE_FDOPEN_PROTO 1
 #cmakedefine SCANDIR_NEEDS_CONST 1
 
 // only for Linux
diff --git a/ktalkd/ConfigureChecks.cmake b/ktalkd/ConfigureChecks.cmake
index 923854b0..d10b5ea4 100644
--- a/ktalkd/ConfigureChecks.cmake
+++ b/ktalkd/ConfigureChecks.cmake
@@ -17,6 +17,9 @@ check_include_file( utmp.h HAVE_UTMP_H )
 check_include_file( utmpx.h HAVE_UTMPX_H )
 
 check_function_exists( vsnprintf HAVE_VSNPRINTF )
+check_function_exists( strerror HAVE_STRERROR )
+check_symbol_exists( strerror "string.h" HAVE_STRERROR_PROTO )
+check_symbol_exists( fdopen "stdio.h" HAVE_FDOPEN_PROTO )
 
 if( ${CMAKE_SYSTEM_NAME} STREQUAL "Linux" )
   set( PROC_FIND_USER 1 CACHE INTERNAL "" FORCE )
diff --git a/ktalkd/mail.local/mail.local.c b/ktalkd/mail.local/mail.local.c
index 9c90d272..c88351dd 100644
--- a/ktalkd/mail.local/mail.local.c
+++ b/ktalkd/mail.local/mail.local.c
@@ -232,8 +232,11 @@ static char copyright[] =
 # define _BSD_VA_LIST_	va_list
 #endif
 
-#if !defined(BSD4_4) && !defined(linux) && !defined(_UNIXWARE)
+#ifndef HAVE_STRERROR_PROTO
 extern char	*strerror __P((int));
+#endif
+
+#ifndef HAVE_FDOPEN_PROTO
 extern FILE	*fdopen __P((int, const char *));
 #endif
 
@@ -831,7 +834,7 @@ e_to_sys(num)
 	}
 }
 
-#if !defined(BSD4_4) && !defined(__osf__) && !defined(__GLIBC__)
+#ifndef HAVE_STRERROR
 
 char *
 strerror(eno)