diff --git a/src/pattern.c b/src/pattern.c
index f6afb9700..2820cf60d 100644
--- a/src/pattern.c
+++ b/src/pattern.c
@@ -487,9 +487,21 @@ struct sample *pattern_process(struct proxy *px, struct session *l4, void *l7,
 		return NULL;
 
 	list_for_each_entry(conv_expr, &expr->conv_exprs, list) {
-		if (!pattern_casts[p->type][conv_expr->conv->in_type](p))
+		/* we want to ensure that p->type can be casted into
+		 * conv_expr->conv->in_type. We have 3 possibilities :
+		 *  - NULL   => not castable.
+		 *  - c_none => nothing to do (let's optimize it)
+		 *  - other  => apply cast and prepare to fail
+		 */
+		if (!pattern_casts[p->type][conv_expr->conv->in_type])
 			return NULL;
 
+		if (pattern_casts[p->type][conv_expr->conv->in_type] != c_none &&
+		    !pattern_casts[p->type][conv_expr->conv->in_type](p))
+			return NULL;
+
+		/* OK cast succeeded */
+
 		/* force the output type after a cast */
 		p->type = conv_expr->conv->in_type;
 		if (!conv_expr->conv->process(conv_expr->arg_p, p))
diff --git a/src/stick_table.c b/src/stick_table.c
index 7bff124e9..a6ae3a297 100644
--- a/src/stick_table.c
+++ b/src/stick_table.c
@@ -600,6 +600,9 @@ struct stktable_key *stktable_fetch_key(struct stktable *t, struct proxy *px, st
 	if (!smp)
 		return NULL;
 
+	if (!pattern_to_key[smp->type][t->type])
+		return NULL;
+
 	static_table_key.key_len = t->key_size;
 	static_table_key.key = pattern_to_key[smp->type][t->type](smp, &static_table_key.data, &static_table_key.key_len);