Index: src/OFString.m
==================================================================
--- src/OFString.m
+++ src/OFString.m
@@ -802,15 +802,20 @@
 	intmax_t num = 0;
 
 	if (string[0] == '-')
 		i++;
 
-	/* FIXME: Add overflow check */
 	for (; i < length; i++) {
-		if (string[i] >= '0' && string[i] <= '9')
-			num = (num * 10) + (string[i] - '0');
-		else
+		if (string[i] >= '0' && string[i] <= '9') {
+			intmax_t newnum = (num * 10) + (string[i] - '0');
+
+			if (newnum < num)
+				@throw [OFOutOfRangeException
+				    newWithClass: isa];
+
+			num = newnum;
+		} else
 			@throw [OFInvalidEncodingException newWithClass: isa];
 	}
 
 	if (string[0] == '-')
 		num *= -1;
@@ -819,11 +824,11 @@
 }
 
 - (intmax_t)hexadecimalValueAsInteger
 {
 	int i = 0;
-	intmax_t num = 0;
+	uintmax_t num = 0;
 
 	if (length == 0)
 		return 0;
 
 	if (length >= 2 && string[0] == '0' && string[1] == 'x')
@@ -832,20 +837,26 @@
 		i = 1;
 
 	if (i == length)
 		@throw [OFInvalidEncodingException newWithClass: isa];
 
-	/* FIXME: Add overflow check */
 	for (; i < length; i++) {
+		uintmax_t newnum;
+
 		if (string[i] >= '0' && string[i] <= '9')
-			num = (num << 4) | (string[i] - '0');
+			newnum = (num << 4) | (string[i] - '0');
 		else if (string[i] >= 'A' && string[i] <= 'F')
-			num = (num << 4) | (string[i] - 'A' + 10);
+			newnum = (num << 4) | (string[i] - 'A' + 10);
 		else if (string[i] >= 'a' && string[i] <= 'f')
-			num = (num << 4) | (string[i] - 'a' + 10);
+			newnum = (num << 4) | (string[i] - 'a' + 10);
 		else
 			@throw [OFInvalidEncodingException newWithClass: isa];
+
+		if (newnum < num)
+			@throw [OFOutOfRangeException newWithClass: isa];
+
+		num = newnum;
 	}
 
 	return num;
 }
 

Index: tests/OFString.m
==================================================================
--- tests/OFString.m
+++ tests/OFString.m
@@ -195,10 +195,11 @@
 	    [[a objectAtIndex: i++] isEqual: @""] &&
 	    [[a objectAtIndex: i++] isEqual: @""])
 
 	TEST(@"-[decimalValueAsInteger]",
 	    [@"1234" decimalValueAsInteger] == 1234 &&
+	    [@"-500" decimalValueAsInteger] == -500 &&
 	    [@"" decimalValueAsInteger] == 0)
 
 	TEST(@"-[hexadecimalValueAsInteger]",
 	    [@"123f" hexadecimalValueAsInteger] == 0x123f &&
 	    [@"0xABcd" hexadecimalValueAsInteger] == 0xABCD &&
@@ -220,10 +221,22 @@
 	    @"-[hexadecimalValueAsInteger] #2", OFInvalidEncodingException,
 	    [@"0x" hexadecimalValueAsInteger])
 	EXPECT_EXCEPTION(@"Detect invalid chars in "
 	    @"-[hexadecimalValueAsInteger] #3", OFInvalidEncodingException,
 	    [@"$" hexadecimalValueAsInteger])
+
+	EXPECT_EXCEPTION(@"Detect out of range in -[decimalValueAsInteger",
+	    OFOutOfRangeException,
+	    [@"12345678901234567890123456789012345678901234567890"
+	     @"12345678901234567890123456789012345678901234567890"
+	    decimalValueAsInteger])
+
+	EXPECT_EXCEPTION(@"Detect out of range in -[hexadecilamValueAsInteger",
+	    OFOutOfRangeException,
+	    [@"0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF"
+	     @"0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF"
+	    hexadecimalValueAsInteger])
 
 	TEST(@"-[md5Hash]", [[@"asdfoobar" md5Hash]
 	    isEqual: @"184dce2ec49b5422c7cfd8728864db4c"])
 
 	TEST(@"-[sha1Hash]", [[@"asdfoobar" sha1Hash]