diff -r b3425cb5ec54 -r 60e4042f2589 core/sm_stringutil.cpp
--- a/core/sm_stringutil.cpp	Sun Apr 20 00:37:20 2014 -0500
+++ b/core/sm_stringutil.cpp	Tue Apr 22 19:40:45 2014 -0700
@@ -213,6 +213,11 @@
 	int significant_digits = 0;	// number of significant digits written
 	const int MAX_SIGNIFICANT_DIGITS = 16;
 
+	if (isnan(fval)) {
+		AddString(buf_p, maxlen, "NaN", width, prec);
+		return;
+	}
+
 	// default precision
 	if (prec < 0)
 	{