Index: src/of_asprintf.m
==================================================================
--- src/of_asprintf.m
+++ src/of_asprintf.m
@@ -97,43 +97,39 @@
 
 #ifndef HAVE_ASPRINTF
 static int
 vasprintf(char **string, const char *format, va_list arguments)
 {
-	int expectedLength, length;
-	va_list argumentsCopy;
-
-	va_copy(argumentsCopy, arguments);
-
-	expectedLength = vsnprintf(NULL, 0, format, argumentsCopy);
-	if (expectedLength == -1)
-		/*
-		 * We have no way to know how large it is. Let's try 64 KB and
-		 * hope.
-		 */
-		expectedLength = 65535;
-
-	if ((*string = malloc((size_t)expectedLength + 1)) == NULL)
-		return -1;
-
-	length = vsnprintf(*string, (size_t)expectedLength + 1,
-	    format, arguments);
-
-	if (length == -1 || length > expectedLength) {
+	size_t length, bufferLength = 128;
+
+	*string = NULL;
+
+	for (;;) {
 		free(*string);
-		*string = NULL;
-		return -1;
+
+		if ((*string = malloc(bufferLength)) == NULL)
+			return -1;
+
+		length = vsnprintf(*string, bufferLength - 1, format,
+		    arguments);
+
+		if (length > 0 && (size_t)length < bufferLength - 1)
+			break;
+
+		if (bufferLength > INT_MAX / 2) {
+			free(*string);
+			return -1;
+		}
+
+		bufferLength <<= 1;
 	}
 
-	/*
-	 * In case we could not determine the size, resize to the actual size
-	 * needed, but ignore any failure to do so.
-	 */
-	if (length < expectedLength) {
-		char *resized;
-
-		if ((resized = realloc(*string, length + 1)) != NULL)
+	if (length != bufferLength - 1) {
+		char *resized = realloc(*string, length + 1);
+
+		/* Ignore if making it smaller failed. */
+		if (resized != NULL)
 			*string = resized;
 	}
 
 	return length;
 }