diff --git a/cp1252/cp1252.c b/cp1252/cp1252.c
index a6d8659..9029c45 100644
--- a/cp1252/cp1252.c
+++ b/cp1252/cp1252.c
@@ -144,7 +144,7 @@ char getCP1252FromUnicode(uint32_t input) {
 			return (char)input;
 		}
 		else {
-			return '\x20';	// SPACE
+			return '\x3F';	// QUESTION MARK
 		}
 	}
 }
@@ -274,4 +274,20 @@ char* getCP1252String(const char* input) {
 	return ret;
 }
 
+char toupperCP1252(char c) {
+	if (c >= 'a' && c <= 'z') {
+		c -= 32;
+	}
+	else if (c == '\x9A' || c == '\x9C' || c == '\x9E') {
+		c -= 16;
+	}
+	else if ((c >= '\xE0' && c <= '\xF6') || (c >= '\xF8' && c <= '\xFE')) {
+		c -= 32;
+	}
+	else if (c == '\xFF') {
+		c = '\x9F';
+	}
+	return c;
+}
+
 #endif //CP1252_INCLUDED
diff --git a/extract-xiso.c b/extract-xiso.c
index edd0bfc..2b1f3a6 100644
--- a/extract-xiso.c
+++ b/extract-xiso.c
@@ -1568,11 +1568,8 @@ int avl_compare_key( const char *in_lhs, const char *in_rhs ) {
 	unsigned char		a, b;
 
 	for ( ;; ) {
-		a = (unsigned char)*in_lhs++;
-		b = (unsigned char)*in_rhs++;
-		
-		if ( a >= 'a' && a <= 'z' ) a -= 32;	// uppercase(a);
-		if ( b >= 'a' && b <= 'z' ) b -= 32;	// uppercase(b);
+		a = (unsigned char)toupperCP1252(*in_lhs++);
+		b = (unsigned char)toupperCP1252(*in_rhs++);
 		
 		if ( a ) {
 			if ( b ) {