diff --git a/src/regexp_nfa.c b/src/regexp_nfa.c
index ff6215e..d779fee 100644
--- a/src/regexp_nfa.c
+++ b/src/regexp_nfa.c
@@ -3218,8 +3218,10 @@
 
     if (nfa_calc_size == FALSE)
     {
-	/* Allocate space for the stack. Max states on the stack : nstate */
+	// Allocate space for the stack. Max states on the stack: "nstate'.
 	stack = (Frag_T *)lalloc((nstate + 1) * sizeof(Frag_T), TRUE);
+	if (stack == NULL)
+	    return NULL;
 	stackp = stack;
 	stack_end = stack + (nstate + 1);
     }