diff --git a/configure.ac b/configure.ac
index 05e83b78..b367be91 100644
--- a/configure.ac
+++ b/configure.ac
@@ -77,6 +77,7 @@ AC_CHECK_LIB(m, log)
 
 AC_CHECK_HEADERS([linux/kd.h dev/isa/spkrio.h dev/speaker/speaker.h])
 AC_CHECK_FUNCS(mmap ioperm)
+AC_CHECK_DECLS([strcasecmp, strncasecmp], [], [], [[#include <strings.h>]])
 
 # OpenBSD I/O i386 library for I/O port access.
 # (64 bit has the same thing with a different name!)
diff --git a/src/doomtype.h b/src/doomtype.h
index e0152179..b659fe69 100644
--- a/src/doomtype.h
+++ b/src/doomtype.h
@@ -21,6 +21,8 @@
 #ifndef __DOOMTYPE__
 #define __DOOMTYPE__
 
+#include "config.h"
+
 #if defined(_MSC_VER) && !defined(__cplusplus)
 #define inline __inline
 #endif
@@ -29,11 +31,15 @@
 // Outside Windows, we use strings.h for str[n]casecmp.
 
 
-#ifdef _WIN32
+#if !HAVE_DECL_STRCASECMP || !HAVE_DECL_STRNCASECMP
 
 #include <string.h>
+#if !HAVE_DECL_STRCASECMP
 #define strcasecmp stricmp
+#endif
+#if !HAVE_DECL_STRNCASECMP
 #define strncasecmp strnicmp
+#endif
 
 #else