Index: configure.ac
==================================================================
--- configure.ac
+++ configure.ac
@@ -38,11 +38,10 @@
 
 		enable_shared="no"
 		enable_threads="no"
 		enable_sockets="no"
 		enable_files="no"
-		ac_cv_snprintf_useful_ret="yes"
 		;;
 	m68k-*-amigaos*)
 		AS_IF([test x"$OBJCFLAGS" = x""], [
 			OBJCFLAGS="-O0"
 		])
@@ -52,11 +51,10 @@
 		LDFLAGS="$LDFLAGS -noixemul"
 
 		enable_files="yes"	# Required for reading ENV:
 		enable_shared="no"
 		supports_amiga_lib="yes"
-		ac_cv_snprintf_useful_ret="yes"
 
 		AS_IF([test x"$enable_amiga_lib" != x"no"], [
 			AC_SUBST(OBJFWRT_AMIGA_LIB, objfwrt68k.library)
 			AC_SUBST(SFDC_TARGET, m68k-amigaos)
 			AC_SUBST(SFD_FILE, amigaos3.sfd)
@@ -828,46 +826,28 @@
 AC_CHECK_LIB(m, fmod, LIBS="$LIBS -lm")
 AC_CHECK_LIB(complex, creal, TESTS_LIBS="$TESTS_LIBS -lcomplex")
 
 AC_CHECK_FUNC(asprintf, [
 	case "$host" in
+		*-*-mingw*)
+			dnl asprintf from MinGW is broken on older Windows
+			dnl versions
+			have_asprintf="no"
+			;;
 		*-psp-*)
-			dnl asprintf is broken on the PSP, but snprintf works.
+			dnl asprintf is broken on the PSP
 			have_asprintf="no"
-			ac_cv_snprintf_useful_ret="yes"
 			;;
 		*)
 			have_asprintf="yes"
 			AC_DEFINE(HAVE_ASPRINTF, 1,
 				[Whether we have asprintf()])
 		;;
 	esac
 ], [
 	have_asprintf="no"
-
-	AC_MSG_CHECKING(whether snprintf returns something useful)
-	AC_CACHE_VAL(ac_cv_snprintf_useful_ret, [
-		AC_TRY_RUN([
-			#include <stdio.h>
-
-			int
-			main()
-			{
-				return (snprintf(NULL, 0, "asd") == 3 ? 0 : 1);
-			}
-		], [
-			ac_cv_snprintf_useful_ret="yes"
-		], [
-			ac_cv_snprintf_useful_ret="no"
-		], [
-			ac_cv_snprintf_useful_ret="no"
-		])
-	])
-	AC_MSG_RESULT($ac_cv_snprintf_useful_ret)
-])
-test x"$have_asprintf" != x"yes" -a x"$ac_cv_snprintf_useful_ret" != x"yes" && \
-	AC_MSG_ERROR(No asprintf and no snprintf returning required space!)
+])
 
 AC_ARG_ENABLE(unicode-tables,
 	AS_HELP_STRING([--disable-unicode-tables], [Disable Unicode tables]))
 AS_IF([test x"$enable_unicode_tables" != x"no"], [
 	AC_DEFINE(OF_HAVE_UNICODE_TABLES, 1,

Index: src/of_asprintf.m
==================================================================
--- src/of_asprintf.m
+++ src/of_asprintf.m
@@ -97,21 +97,47 @@
 
 #ifndef HAVE_ASPRINTF
 static int
 vasprintf(char **string, const char *format, va_list arguments)
 {
-	int length;
+	int expectedLength, length;
 	va_list argumentsCopy;
 
 	va_copy(argumentsCopy, arguments);
 
-	if ((length = vsnprintf(NULL, 0, format, argumentsCopy)) < 0)
-		return length;
-	if ((*string = malloc((size_t)length + 1)) == NULL)
+	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) {
+		free(*string);
+		*string = NULL;
 		return -1;
+	}
 
-	return vsnprintf(*string, (size_t)length + 1, format, arguments);
+	/*
+	 * 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)
+			*string = resized;
+	}
+
+	return length;
 }
 
 static int
 asprintf(char **string, const char *format, ...)
 {
@@ -549,10 +575,13 @@
 		default:
 			return false;
 		}
 
 #ifndef HAVE_ASPRINTF_L
+		if (tmpLen == -1)
+			return false;
+
 		/*
 		 * If there's no asprintf_l, we have no other choice than to
 		 * use this ugly hack to replace the locale's decimal point
 		 * back to ".".
 		 */