diff --git a/common/errors.c b/common/errors.c
index c7a8448d..94ce0c0b 100644
--- a/common/errors.c
+++ b/common/errors.c
@@ -2,22 +2,27 @@
 #include "uipriv.h"
 #include "testhooks.h"
 
+#define maxErrorBuf 256
+#define conststrlen(s) ((sizeof (s) / sizeof (char)) - 1)
+#define errorBufSize(prefix, suffix) (conststrlen(prefix) + maxErrorBuf + conststrlen(suffix) + 1)
+
 #define internalErrorPrefix "libui internal error"
 // TODO add debugging advice?
 #define internalErrorSuffix "This likely means there is a bug in libui itself. Contact the libui authors."
+#define internalErrorBufSize errorBufSize(internalErrorPrefix, internalErrorSuffix)
 
 void uiprivInternalError(const char *fmt, ...)
 {
 	va_list ap;
-	char buf[256];
+	char buf[internalErrorBufSize];
 	int n;
 
 	va_start(ap, fmt);
-	n = uiprivVsnprintf(buf, 256, fmt, ap);
+	n = uiprivVsnprintf(buf, internalErrorBufSize, fmt, ap);
 	va_end(ap);
 	if (n < 0)
 		uiprivReportError(internalErrorPrefix, "internal error string has encoding error", internalErrorSuffix, true);
-	if (n >= 256)
+	if (n >= internalErrorBufSize)
 		uiprivReportError(internalErrorPrefix, "internal error string too long", internalErrorSuffix, true);
 	uiprivReportError(internalErrorPrefix, buf, internalErrorSuffix, true);
 }
@@ -25,6 +30,7 @@ void uiprivInternalError(const char *fmt, ...)
 #define programmerErrorPrefix "libui programmer error"
 // TODO add debugging advice?
 #define programmerErrorSuffix "This likely means you are using libui incorrectly. Check your source code and try again. If you have received this warning in error, contact the libui authors."
+#define programmerErrorBufSize errorBufSize(programmerErrorPrefix, programmerErrorSuffix)
 
 static uiprivTestHookReportProgrammerErrorFunc reportProgrammerErrorTestHook = NULL;
 static void *reportProgrammerErrorTestHookData = NULL;
@@ -38,14 +44,14 @@ void uiprivTestHookReportProgrammerError(uiprivTestHookReportProgrammerErrorFunc
 void uiprivProgrammerError(const char *fmt, ...)
 {
 	va_list ap;
+	char buf[programmerErrorBufSize];
 	int n;
-	char buf[256];
 
 	va_start(ap, fmt);
-	n = uiprivVsnprintf(buf, 256, fmt, ap);
+	n = uiprivVsnprintf(buf, programmerErrorBufSize, fmt, ap);
 	if (n < 0)
 		uiprivInternalError("programmer error has encoding error");
-	if (n >= 256)
+	if (n >= programmerErrorBufSize)
 		uiprivInternalError("programmer error string too long (%d)", n);
 	va_end(ap);
 	if (reportProgrammerErrorTestHook != NULL) {