diff --git a/src/gflags_reporting.cc b/src/gflags_reporting.cc
index 7f49935..d834fe2 100644
--- a/src/gflags_reporting.cc
+++ b/src/gflags_reporting.cc
@@ -122,11 +122,12 @@ string DescribeOneFlag(const CommandLineFlagInfo& flag) {
                 flag.name.c_str(),
                 flag.description.c_str());
   const char* c_string = main_part.c_str();
-  size_t chars_left = main_part.length();
+  int chars_left = main_part.length();
   string final_string = "";
   int chars_in_line = 0;  // how many chars in current line so far?
   while (1) {
-    assert(chars_left == strlen(c_string));  // Unless there's a \0 in there?
+    assert(static_cast<size_t>(chars_left)
+            == strlen(c_string));  // Unless there's a \0 in there?
     const char* newline = strchr(c_string, '\n');
     if (newline == NULL && chars_in_line+chars_left < kLineLength) {
       // The whole remainder of the string fits on this line