diff --git a/src/common/parser/ApcParser.test.ts b/src/common/parser/ApcParser.test.ts
index b27b40039..563ddbeab 100644
--- a/src/common/parser/ApcParser.test.ts
+++ b/src/common/parser/ApcParser.test.ts
@@ -21,7 +21,7 @@ function identifier(id: IFunctionIdentifier): number {
       throw new Error('only one byte as prefix supported');
     }
     res = id.prefix.charCodeAt(0);
-    if (res && 0x3c > res || res > 0x3f) {
+    if (res < 0x3c || res > 0x3f) {
       throw new Error('prefix must be in range 0x3c .. 0x3f');
     }
   }
diff --git a/src/common/parser/DcsParser.test.ts b/src/common/parser/DcsParser.test.ts
index 459bc8961..5fa7b9416 100644
--- a/src/common/parser/DcsParser.test.ts
+++ b/src/common/parser/DcsParser.test.ts
@@ -22,7 +22,7 @@ function identifier(id: IFunctionIdentifier): number {
       throw new Error('only one byte as prefix supported');
     }
     res = id.prefix.charCodeAt(0);
-    if (res && 0x3c > res || res > 0x3f) {
+    if (res < 0x3c || res > 0x3f) {
       throw new Error('prefix must be in range 0x3c .. 0x3f');
     }
   }
diff --git a/src/common/parser/EscapeSequenceParser.ts b/src/common/parser/EscapeSequenceParser.ts
index 87844113a..009ed6ccb 100644
--- a/src/common/parser/EscapeSequenceParser.ts
+++ b/src/common/parser/EscapeSequenceParser.ts
@@ -342,7 +342,7 @@ export class EscapeSequenceParser extends Disposable implements IEscapeSequenceP
         throw new Error('only one byte as prefix supported');
       }
       res = id.prefix.charCodeAt(0);
-      if (res && 0x3c > res || res > 0x3f) {
+      if (res < 0x3c || res > 0x3f) {
         throw new Error('prefix must be in range 0x3c .. 0x3f');
       }
     }
diff --git a/src/common/parser/Params.test.ts b/src/common/parser/Params.test.ts
index 3bd67d397..a30b1376c 100644
--- a/src/common/parser/Params.test.ts
+++ b/src/common/parser/Params.test.ts
@@ -199,13 +199,13 @@ describe('Params', () => {
     it('reject params lesser -1', () => {
       const params = new Params();
       params.addParam(-1);
-      assert.throws(() => params.addParam(-2), 'values lesser than -1 are not allowed');
+      assert.throws(() => params.addParam(-2), 'values less than -1 are not allowed');
     });
     it('reject subparams lesser -1', () => {
       const params = new Params();
       params.addParam(-1);
       params.addSubParam(-1);
-      assert.throws(() => params.addSubParam(-2), 'values lesser than -1 are not allowed');
+      assert.throws(() => params.addSubParam(-2), 'values less than -1 are not allowed');
       assert.deepEqual(params.toArray(), [-1, [-1]]);
     });
     it('clamp parsed params', () => {
diff --git a/src/common/parser/Params.ts b/src/common/parser/Params.ts
index 76dbe2b3d..76c6bee5a 100644
--- a/src/common/parser/Params.ts
+++ b/src/common/parser/Params.ts
@@ -162,7 +162,7 @@ export class Params implements IParams {
       return;
     }
     if (value < -1) {
-      throw new Error('values lesser than -1 are not allowed');
+      throw new Error('values less than -1 are not allowed');
     }
     this._subParamsIdx[this.length] = this._subParamsLength << 8 | this._subParamsLength;
     this.params[this.length++] = value > Constants.MAX_VALUE ? Constants.MAX_VALUE : value;
@@ -185,7 +185,7 @@ export class Params implements IParams {
       return;
     }
     if (value < -1) {
-      throw new Error('values lesser than -1 are not allowed');
+      throw new Error('values less than -1 are not allowed');
     }
     this._subParams[this._subParamsLength++] = value > Constants.MAX_VALUE ? Constants.MAX_VALUE : value;
     this._subParamsIdx[this.length - 1]++;