diff --git a/src/regexp.h b/src/regexp.h
index fa3ff42..c2fafef 100644
--- a/src/regexp.h
+++ b/src/regexp.h
@@ -81,7 +81,7 @@
 
 /*
  * Structure representing a NFA state.
- * A NFA state may have no outgoing edge, when it is a NFA_MATCH state.
+ * An NFA state may have no outgoing edge, when it is a NFA_MATCH state.
  */
 typedef struct nfa_state nfa_state_T;
 struct nfa_state