diff --git a/src/VSpace.cpp b/src/VSpace.cpp
index 06799263f4..46f39bfeae 100644
--- a/src/VSpace.cpp
+++ b/src/VSpace.cpp
@@ -244,27 +244,21 @@ bool isValidGlueLength(string const & data, GlueLength * result)
 	}
 	// end of hack
 
-	int  pattern_index = 0;
-	int  table_index = 0;
-	char pattern[22]; // 20 + 1 for pattern[20], + 1 for '\0'
-
-	number_index = 1;
-	unit_index = 1;  // entries at index 0 are sentinels
-
 	// construct "pattern" from "data"
+	size_t const pattern_max_size = 20;
+	string pattern;
 	while (!isEndOfData(buffer)) {
-		if (pattern_index > (sizeof(pattern) - 2))
+		if (pattern.size() > pattern_max_size)
 			return false;
-		pattern[pattern_index] = nextToken(buffer);
-		if (pattern[pattern_index] == 'E')
+		char const c = nextToken(buffer);
+		if (c == 'E')
 			return false;
-		++pattern_index;
+		pattern.push_back(c);
 	}
-	pattern[pattern_index] = '\0';
 
 	// search "pattern" in "table"
-	table_index = 0;
-	while (strcmp(pattern, table[table_index].pattern)) {
+	size_t table_index = 0;
+	while (pattern != table[table_index].pattern) {
 		++table_index;
 		if (!*table[table_index].pattern)
 			return false;