diff --git a/filter/decl.m4 b/filter/decl.m4
index 5b35b672..7c863bdc 100644
--- a/filter/decl.m4
+++ b/filter/decl.m4
@@ -200,7 +200,7 @@ FID_INTERPRET_BODY()')
 #	Executing another filter line. This replaces the recursion
 #	that was needed in the former implementation.
 m4_define(LINEX, `FID_INTERPRET_EXEC()LINEX_($1)FID_INTERPRET_NEW()return $1 FID_INTERPRET_BODY()')
-m4_define(LINEX_, `do {
+m4_define(LINEX_, `do if ($1) {
   fstk->estk[fstk->ecnt].pos = 0;
   fstk->estk[fstk->ecnt].line = $1;
   fstk->estk[fstk->ecnt].ventry = fstk->vcnt;
@@ -227,9 +227,7 @@ if (!f_same(f1->fl$1, f2->fl$1)) return 0;
 FID_ITERATE_BODY()m4_dnl
 if (whati->fl$1) BUFFER_PUSH(fit->lines) = whati->fl$1;
 FID_INTERPRET_EXEC()m4_dnl
-do { if (whati->fl$1) {
-  LINEX_(whati->fl$1);
-} } while(0)
+LINEX_(whati->fl$1)
 FID_INTERPRET_NEW()m4_dnl
 return whati->f$1
 FID_INTERPRET_BODY()')
diff --git a/filter/f-inst.c b/filter/f-inst.c
index e4b47ff4..33436853 100644
--- a/filter/f-inst.c
+++ b/filter/f-inst.c
@@ -1327,7 +1327,6 @@
 	FID_HIC(,break,return NULL);
       }
     }
-    /* It is actually possible to have t->data NULL */
 
     LINEX(t->data);
   }
diff --git a/filter/test.conf b/filter/test.conf
index 600c551e..e9e3af89 100644
--- a/filter/test.conf
+++ b/filter/test.conf
@@ -38,6 +38,18 @@ bt_test_same(onef, onef, 1);
 bt_test_same(onef, oneg, 1);
 bt_test_same(onef, twof, 0);
 
+/*
+ *	Testing filter corner cases
+ *	---------------------------
+ */
+
+function t_nothing() {}
+bt_test_suite(t_nothing, "Testing nothing");
+
+function t_metanothing() { t_nothing(); }
+bt_test_suite(t_metanothing, "Testing meta nothing");
+
+
 /*
  * 	Testing boolean expressions
  * 	---------------------------
@@ -76,6 +88,14 @@ bt_test_suite(t_bool, "Testing boolean expressions");
  *	----------------
  */
 
+function aux_t_int(int t; int u)
+{
+	case t {
+		1: {}
+		else: {}
+	}
+}
+
 define four = 4;
 define xyzzy = (120+10);
 define '1a-a1' = (xyzzy-100);
@@ -120,7 +140,10 @@ function t_int()
 		else: bt_assert(false);
 	}
 
-
+	aux_t_int(1, 2);
+	aux_t_int(1, 3);
+	aux_t_int(2, 3);
+	aux_t_int(2, 2);
 }
 
 bt_test_suite(t_int, "Testing integers");