diff --git a/historic/jam/src/variable.c b/historic/jam/src/variable.c
index 36647e973..1399723b0 100644
--- a/historic/jam/src/variable.c
+++ b/historic/jam/src/variable.c
@@ -203,6 +203,12 @@ var_string(
 		*out++ = *in++;
 	    }
 
+        /* Add zero to 'out' so that 'lastword' is correctly zero-terminated. */
+        if (out >= oute)
+            return -1;
+        /* Don't increment, intentionally. */
+        *out= '\0';
+           
 	    /* If a variable encountered, expand it and and embed the */
 	    /* space-separated members of the list in the output. */
 
diff --git a/jam_src/variable.c b/jam_src/variable.c
index 36647e973..1399723b0 100644
--- a/jam_src/variable.c
+++ b/jam_src/variable.c
@@ -203,6 +203,12 @@ var_string(
 		*out++ = *in++;
 	    }
 
+        /* Add zero to 'out' so that 'lastword' is correctly zero-terminated. */
+        if (out >= oute)
+            return -1;
+        /* Don't increment, intentionally. */
+        *out= '\0';
+           
 	    /* If a variable encountered, expand it and and embed the */
 	    /* space-separated members of the list in the output. */