--- a/src/data.cc
+++ b/src/data.cc
@@ -33,6 +33,8 @@
 #include <config.h>
 #endif
 
+#include <string>
+
 #include "defun.h"
 #include "error.h"
 #include "gripes.h"
@@ -804,7 +806,8 @@
       retval = 0.0;
       if (args(0).is_map () && args(1).is_string ())
 	{
-	  const char *s = args(1).string_value ();
+	  string tstr = args(1).string_value ();
+	  const char *s = tstr.c_str ();
 	  tree_constant tmp = args(0).lookup_map_element (s, 0, 1);
 	  retval = (double) tmp.is_defined ();
 	}