diff --git a/src/css/codemirror.css b/src/css/codemirror.css
index 9733fe4ec..e736dd4ce 100644
--- a/src/css/codemirror.css
+++ b/src/css/codemirror.css
@@ -191,7 +191,7 @@
     align-items: center;
     display: inline-flex;
     flex-grow: 0;
-    font-size: 95%;
+    font-size: var(--font-size-smaller);
     min-width: 6em;
     visibility: hidden;
     }
@@ -206,15 +206,17 @@
     }
 
 .cm-linter-widget {
+    align-items: center;
     display: none;
     flex-grow: 1;
     }
 .cm-linter-widget.hasErrors {
-    display: initial;
+    display: inline-flex;
     }
 .cm-linter-widget .cm-linter-widget-count {
     color: var(--accent-surface-1);
         fill: var(--accent-surface-1);
+    font-size: var(--font-size-smaller);
     }
 
 .cm-searching.cm-overlay {
diff --git a/src/js/codemirror/ubo-static-filtering.js b/src/js/codemirror/ubo-static-filtering.js
index 511b7b78e..d7d3755a3 100644
--- a/src/js/codemirror/ubo-static-filtering.js
+++ b/src/js/codemirror/ubo-static-filtering.js
@@ -729,12 +729,21 @@ CodeMirror.registerHelper('fold', 'ubo-static-filtering', (( ) => {
         if ( astParser.isCosmeticFilter() && astParser.result.error ) {
             return `${error}: ${astParser.result.error}`;
         }
-        if ( astParser.astError === sfp.AST_ERROR_BAD_REGEX ) {
+        if ( astParser.astError === sfp.AST_ERROR_REGEX ) {
             return `${error}: Bad regular expression`;
         }
-        if ( astParser.astError === sfp.AST_ERROR_BAD_PATTERN ) {
+        if ( astParser.astError === sfp.AST_ERROR_PATTERN ) {
             return `${error}: Bad pattern`;
         }
+        if ( astParser.astError === sfp.AST_ERROR_DOMAIN_NAME ) {
+            return `${error}: Bad domain name`;
+        }
+        if ( astParser.astError === sfp.AST_ERROR_OPTION_DUPLICATE ) {
+            return `${error}: Duplicate filter option`;
+        }
+        if ( astParser.astError === sfp.AST_ERROR_OPTION_UNKNOWN ) {
+            return `${error}: Unsupported filter option`;
+        }
         return error;
     };
 
diff --git a/src/js/static-filtering-parser.js b/src/js/static-filtering-parser.js
index ccb26610c..54d0c082a 100644
--- a/src/js/static-filtering-parser.js
+++ b/src/js/static-filtering-parser.js
@@ -92,8 +92,11 @@ export const AST_FLAG_HAS_OPTIONS                   = 1 << iota++;
 
 iota = 0;
 export const AST_ERROR_NONE                         = 1 << iota++;
-export const AST_ERROR_BAD_REGEX                    = 1 << iota++;
-export const AST_ERROR_BAD_PATTERN                  = 1 << iota++;
+export const AST_ERROR_REGEX                        = 1 << iota++;
+export const AST_ERROR_PATTERN                      = 1 << iota++;
+export const AST_ERROR_DOMAIN_NAME                  = 1 << iota++;
+export const AST_ERROR_OPTION_DUPLICATE             = 1 << iota++;
+export const AST_ERROR_OPTION_UNKNOWN               = 1 << iota++;
 
 iota = 0;
 const NODE_RIGHT_INDEX                              = iota++;
@@ -1278,6 +1281,7 @@ export class AstFilterParser {
                     realBad = isNegated || hasValue;
                     break;
                 case NODE_TYPE_NET_OPTION_NAME_UNKNOWN:
+                    this.astError = AST_ERROR_OPTION_UNKNOWN;
                     realBad = true;
                     break;
                 case NODE_TYPE_NET_OPTION_NAME_WEBRTC:
@@ -1481,7 +1485,7 @@ export class AstFilterParser {
                 }
             } else {
                 this.astTypeFlavor = AST_TYPE_NETWORK_PATTERN_BAD;
-                this.astError = AST_ERROR_BAD_REGEX;
+                this.astError = AST_ERROR_REGEX;
                 this.addFlags(AST_FLAG_HAS_ERROR);
                 this.addNodeFlags(next, NODE_FLAG_ERROR);
             }
@@ -1602,7 +1606,7 @@ export class AstFilterParser {
         if ( normal === undefined ) {
             this.astTypeFlavor = AST_TYPE_NETWORK_PATTERN_BAD;
             this.addFlags(AST_FLAG_HAS_ERROR);
-            this.astError = AST_ERROR_BAD_PATTERN;
+            this.astError = AST_ERROR_PATTERN;
             this.addNodeFlags(next, NODE_FLAG_ERROR);
         } else if ( normal === '' || pattern === '*' ) {
             this.astTypeFlavor = AST_TYPE_NETWORK_PATTERN_ANY;
@@ -1813,6 +1817,7 @@ export class AstFilterParser {
         if ( this.getBranchFromType(nodeOptionType) !== 0 ) {
             this.addNodeFlags(parent, NODE_FLAG_ERROR);
             this.addFlags(AST_FLAG_HAS_ERROR);
+            this.astError = AST_ERROR_OPTION_DUPLICATE;
         } else {
             this.addNodeToRegister(nodeOptionType, parent);
         }
@@ -1956,6 +1961,7 @@ export class AstFilterParser {
                 } else {
                     this.addNodeFlags(parent, NODE_FLAG_ERROR);
                     this.addFlags(AST_FLAG_HAS_ERROR);
+                    this.astError = AST_ERROR_DOMAIN_NAME;
                 }
             }
             if ( head === 0 ) {