diff --git a/src/EscapeSequenceParser.test.ts b/src/EscapeSequenceParser.test.ts
index 1c5b6d6c..c40a2b36 100644
--- a/src/EscapeSequenceParser.test.ts
+++ b/src/EscapeSequenceParser.test.ts
@@ -11,6 +11,30 @@ function r(a: number, b: number): string[] {
     return arr;
 }
 
+class TestEscapeSequenceParser extends EscapeSequenceParser {
+    public get osc(): string {
+        return this._osc;
+    }
+    public set osc(value: string) {
+        this._osc = value;
+    }
+    public get params(): number[] {
+        return this._params;
+    }
+    public set params(value: number[]) {
+        this._params = value;
+    }
+    public get collect(): string {
+        return this._collect;
+    }
+    public set collect(value: string) {
+        this._collect = value;
+    }
+    public mockActiveDcsHandler(): void {
+        this._activeDcsHandler = this._dcsHandlerFb;
+    }
+}
+
 let testTerminal: any = {
     calls: [],
     clear: function (): void {
@@ -75,7 +99,7 @@ let states: number[] = [
 ];
 let state: any;
 
-let parser = new EscapeSequenceParser();
+let parser = new TestEscapeSequenceParser();
 parser.setPrintHandler(testTerminal.print.bind(testTerminal));
 parser.setCsiHandlerFallback((...params: any[]) => {
     testTerminal.actionCSI(params[0], params[1], String.fromCharCode(params[2]));
@@ -872,6 +896,7 @@ describe('EscapeSequenceParser', function(): void {
             puts.concat(r(0x20, 0x7f));
             for (let i = 0; i < puts.length; ++i) {
                 parser.currentState = ParserState.DCS_PASSTHROUGH;
+                parser.mockActiveDcsHandler();
                 parser.parse(puts[i]);
                 chai.expect(parser.currentState).equal(ParserState.DCS_PASSTHROUGH);
                 testTerminal.compare([['dcs put', puts[i]]]);
diff --git a/src/EscapeSequenceParser.ts b/src/EscapeSequenceParser.ts
index 175bf444..cd21977e 100644
--- a/src/EscapeSequenceParser.ts
+++ b/src/EscapeSequenceParser.ts
@@ -207,10 +207,9 @@ export class EscapeSequenceParser implements IEscapeSequenceParser {
   public currentState: number;
 
   // buffers over several parse calls
-  // FIXME: make those protected (needs workaround in tests)
-  public osc: string;
-  public params: number[];
-  public collect: string;
+  protected _osc: string;
+  protected _params: number[];
+  protected _collect: string;
 
   // handler lookup containers
   protected _printHandler: (data: string, start: number, end: number) => void;
@@ -234,9 +233,9 @@ export class EscapeSequenceParser implements IEscapeSequenceParser {
   constructor(readonly transitions: TransitionTable = VT500_TRANSITION_TABLE) {
     this.initialState = ParserState.GROUND;
     this.currentState = this.initialState;
-    this.osc = '';
-    this.params = [0];
-    this.collect = '';
+    this._osc = '';
+    this._params = [0];
+    this._collect = '';
 
     // set default fallback handlers and handler lookup containers
     this._printHandlerFb = (data, start, end): void => { };
@@ -325,9 +324,9 @@ export class EscapeSequenceParser implements IEscapeSequenceParser {
    */
   reset(): void {
     this.currentState = this.initialState;
-    this.osc = '';
-    this.params = [0];
-    this.collect = '';
+    this._osc = '';
+    this._params = [0];
+    this._collect = '';
     this._activeDcsHandler = null;
   }
 
@@ -342,9 +341,9 @@ export class EscapeSequenceParser implements IEscapeSequenceParser {
     let currentState = this.currentState;
     let print = -1;
     let dcs = -1;
-    let osc = this.osc;
-    let collect = this.collect;
-    let params = this.params;
+    let osc = this._osc;
+    let collect = this._collect;
+    let params = this._params;
     const table: Uint8Array | number[] = this.transitions.table;
     let dcsHandler: IDcsHandler | null = this._activeDcsHandler;
     let callback: Function | null = null;
@@ -529,9 +528,9 @@ export class EscapeSequenceParser implements IEscapeSequenceParser {
     }
 
     // save non pushable buffers
-    this.osc = osc;
-    this.collect = collect;
-    this.params = params;
+    this._osc = osc;
+    this._collect = collect;
+    this._params = params;
 
     // save active dcs handler reference
     this._activeDcsHandler = dcsHandler;