diff --git a/src/js/pagestore.js b/src/js/pagestore.js
index 3d6d4a531..0b332a604 100644
--- a/src/js/pagestore.js
+++ b/src/js/pagestore.js
@@ -526,7 +526,7 @@ PageStore.prototype.filterRequest = function(context) {
 
     // Static filtering never override dynamic filtering
     if ( result === '' || result.charAt(1) === 'n' ) {
-        if ( µb.staticNetFilteringEngine.matchString(context) ) {
+        if ( µb.staticNetFilteringEngine.matchString(context) !== undefined ) {
             result = µb.staticNetFilteringEngine.toResultString(µb.logger.isEnabled());
         }
     }
@@ -568,7 +568,7 @@ PageStore.prototype.filterRequestNoCache = function(context) {
 
     // Static filtering never override dynamic filtering
     if ( result === '' || result.charAt(1) === 'n' ) {
-        if ( µb.staticNetFilteringEngine.matchString(context) ) {
+        if ( µb.staticNetFilteringEngine.matchString(context) !== undefined ) {
             result = µb.staticNetFilteringEngine.toResultString(µb.logger.isEnabled());
         }
     }
diff --git a/src/js/static-net-filtering.js b/src/js/static-net-filtering.js
index 52f968b84..52c80e88a 100644
--- a/src/js/static-net-filtering.js
+++ b/src/js/static-net-filtering.js
@@ -2238,7 +2238,7 @@ FilterContainer.prototype.matchStringExactType = function(context, requestURL, r
     // Be prepared to support unknown types
     var type = typeNameToTypeValue[requestType] || 0;
     if ( type === 0 ) {
-        return false;
+        return undefined;
     }
 
     var categories = this.categories;
@@ -2280,7 +2280,7 @@ FilterContainer.prototype.matchStringExactType = function(context, requestURL, r
 
     // If there is no block filter, no need to test against allow filters
     if ( this.fRegister === null ) {
-        return false;
+        return undefined;
     }
 
     // Test against allow filters
@@ -2412,7 +2412,7 @@ FilterContainer.prototype.matchString = function(context) {
 
     // If there is no block filter, no need to test against allow filters
     if ( this.fRegister === null ) {
-        return false;
+        return undefined;
     }
 
     // Test against allow filters
diff --git a/src/js/tab.js b/src/js/tab.js
index c195bbbb0..1c28b5007 100644
--- a/src/js/tab.js
+++ b/src/js/tab.js
@@ -507,7 +507,7 @@ vAPI.tabs.onPopup = function(details) {
         µb.getNetFilteringSwitch(openerURL) &&
         µb.getNetFilteringSwitch(targetURL)
     ) {
-        if ( µb.staticNetFilteringEngine.matchStringExactType(context, targetURL, 'popup') ) {
+        if ( µb.staticNetFilteringEngine.matchStringExactType(context, targetURL, 'popup') !== undefined ) {
             result = µb.staticNetFilteringEngine.toResultString(loggerEnabled);
         }
     }
diff --git a/src/js/traffic.js b/src/js/traffic.js
index 0a458f0d8..f5db33fb1 100644
--- a/src/js/traffic.js
+++ b/src/js/traffic.js
@@ -185,7 +185,7 @@ var onBeforeRootFrameRequest = function(details) {
 
     // Filtering
     if ( result === '' ) {
-        if ( µb.staticNetFilteringEngine.matchString(context) ) {
+        if ( µb.staticNetFilteringEngine.matchString(context) !== undefined ) {
             // We always need the long-form result here.
             result = µb.staticNetFilteringEngine.toResultString(true);
             // https://github.com/chrisaljoudi/uBlock/issues/1128