diff --git a/shell/msh.c b/shell/msh.c
index 2fb0df7..14e8758 100644
--- a/shell/msh.c
+++ b/shell/msh.c
@@ -4290,7 +4290,7 @@
 			}
 
 			var_name[var_index++] = *src++;
-			while (isalnum(*src))
+			while (isalnum(*src) || *src=='_')
 				var_name[var_index++] = *src++;
 			var_name[var_index] = 0;