diff --git a/src/common/parser/Constants.ts b/src/common/parser/Constants.ts
index fec3cee3..b066654c 100644
--- a/src/common/parser/Constants.ts
+++ b/src/common/parser/Constants.ts
@@ -21,7 +21,9 @@ export const enum ParserState {
   DCS_IGNORE = 11,
   DCS_INTERMEDIATE = 12,
   DCS_PASSTHROUGH = 13,
-  APC_STRING = 14
+  APC_STRING = 14,
+  // Number of states. States must be continuous and this must be LAST_STATE + 1.
+  STATE_LENGTH = 15
 }
 
 /**
diff --git a/src/common/parser/EscapeSequenceParser.ts b/src/common/parser/EscapeSequenceParser.ts
index ef627c9d..d11579e8 100644
--- a/src/common/parser/EscapeSequenceParser.ts
+++ b/src/common/parser/EscapeSequenceParser.ts
@@ -90,7 +90,7 @@ export const VT500_TRANSITION_TABLE = (function (): TransitionTable {
   EXECUTABLES.push(0x19);
   EXECUTABLES.push.apply(EXECUTABLES, r(0x1c, 0x20));
 
-  const states: number[] = r(ParserState.GROUND, ParserState.APC_STRING + 1);
+  const states: number[] = r(ParserState.GROUND, ParserState.STATE_LENGTH);
   let state: any;
 
   // set default transition