--- a/inc/htmshell.h
+++ b/inc/htmshell.h
@@ -85,7 +85,7 @@ void htmlBadVar(char *varName);
 void htmlImage(char *fileName, int width, int height); 
 /* Display centered image file. */
 
-jmp_buf htmlRecover;  /* Error recovery jump. Exposed for cart's use. */
+extern jmp_buf htmlRecover;  /* Error recovery jump. Exposed for cart's use. */
 
 void htmlVaWarn(char *format, va_list args);
 /* Write an error message.  (Generally you just call warn() or errAbort().