diff --git a/src/js/static-filtering-parser.js b/src/js/static-filtering-parser.js
index e2854aea8..764c6b38f 100644
--- a/src/js/static-filtering-parser.js
+++ b/src/js/static-filtering-parser.js
@@ -866,6 +866,7 @@ const Parser = class {
         return i;
     }
 
+    // Important: the from-to indices are inclusive.
     strFromSlices(from, to) {
         return this.raw.slice(
             this.slices[from+1],
@@ -2396,10 +2397,17 @@ const NetOptionsIterator = class {
         // `queryprune=`:  only for network requests.
         {
             const i = this.tokenPos[OPTTokenQueryprune];
-            if ( i !== -1 && hasBits(allBits, OPTNonNetworkType) ) {
-                optSlices[i] = OPTTokenInvalid;
-                if ( this.interactive ) {
-                    this.parser.errorSlices(optSlices[i+1], optSlices[i+5]);
+            if ( i !== -1 ) {
+                if ( hasBits(allBits, OPTNonNetworkType) ) {
+                    optSlices[i] = OPTTokenInvalid;
+                    if ( this.interactive ) {
+                        this.parser.errorSlices(optSlices[i+1], optSlices[i+5]);
+                    }
+                } else if ( this.validateQueryPruneArg(i) === false ) {
+                    optSlices[i] = OPTTokenInvalid;
+                    if ( this.interactive ) {
+                        this.parser.errorSlices(optSlices[i+4], optSlices[i+5]);
+                    }
                 }
             }
         }
@@ -2442,6 +2450,20 @@ const NetOptionsIterator = class {
         this.readPtr = i + 6;
         return this;
     }
+    validateQueryPruneArg(i) {
+        let val = this.parser.strFromSlices(
+            this.optSlices[i+4],
+            this.optSlices[i+5] - 3
+        );
+        if ( val.startsWith('|') ) { val = `^${val.slice(1)}`; }
+        if ( val.endsWith('|') ) { val = `${val.slice(0,-1)}$`; }
+        try {
+            void new RegExp(val);
+        } catch(ex) {
+            return false;
+        }
+        return true;
+    }
 };
 
 /******************************************************************************/