diff --git a/ext/bg/js/options.js b/ext/bg/js/options.js
index 1b2d5e1a..df95aae9 100644
--- a/ext/bg/js/options.js
+++ b/ext/bg/js/options.js
@@ -221,6 +221,7 @@ function optionsSetDefaults(options) {
             modifier: 'shift',
             deepDomScan: false,
             popupNestingMaxDepth: 0,
+            enableOnPopupExpressions: false,
             enableOnSearchPage: true
         },
 
diff --git a/ext/bg/js/settings.js b/ext/bg/js/settings.js
index 5472c7bd..83f4528c 100644
--- a/ext/bg/js/settings.js
+++ b/ext/bg/js/settings.js
@@ -48,6 +48,7 @@ async function formRead() {
     optionsNew.scanning.alphanumeric = $('#search-alphanumeric').prop('checked');
     optionsNew.scanning.autoHideResults = $('#auto-hide-results').prop('checked');
     optionsNew.scanning.deepDomScan = $('#deep-dom-scan').prop('checked');
+    optionsNew.scanning.enableOnPopupExpressions = $('#enable-scanning-of-popup-expressions').prop('checked');
     optionsNew.scanning.enableOnSearchPage = $('#enable-scanning-on-search-page').prop('checked');
     optionsNew.scanning.delay = parseInt($('#scan-delay').val(), 10);
     optionsNew.scanning.length = parseInt($('#scan-length').val(), 10);
@@ -191,6 +192,7 @@ async function onReady() {
     $('#search-alphanumeric').prop('checked', options.scanning.alphanumeric);
     $('#auto-hide-results').prop('checked', options.scanning.autoHideResults);
     $('#deep-dom-scan').prop('checked', options.scanning.deepDomScan);
+    $('#enable-scanning-of-popup-expressions').prop('checked', options.scanning.enableOnPopupExpressions);
     $('#enable-scanning-on-search-page').prop('checked', options.scanning.enableOnSearchPage);
     $('#scan-delay').val(options.scanning.delay);
     $('#scan-length').val(options.scanning.length);
diff --git a/ext/bg/settings.html b/ext/bg/settings.html
index 0005efa6..85b7ee5f 100644
--- a/ext/bg/settings.html
+++ b/ext/bg/settings.html
@@ -192,6 +192,10 @@
                     <label><input type="checkbox" id="auto-hide-results"> Automatically hide results</label>
                 </div>
 
+                <div class="checkbox options-advanced">
+                    <label><input type="checkbox" id="enable-scanning-of-popup-expressions"> Enable scanning of popup expressions</label>
+                </div>
+
                 <div class="checkbox">
                     <label><input type="checkbox" id="enable-scanning-on-search-page"> Enable scanning on search page</label>
                 </div>
diff --git a/ext/fg/js/frontend.js b/ext/fg/js/frontend.js
index 3605dffd..f59ea318 100644
--- a/ext/fg/js/frontend.js
+++ b/ext/fg/js/frontend.js
@@ -18,7 +18,7 @@
 
 
 class Frontend {
-    constructor(popup) {
+    constructor(popup, ignoreNodes) {
         this.popup = popup;
         this.popupTimer = null;
         this.mouseDownLeft = false;
@@ -26,6 +26,7 @@ class Frontend {
         this.textSourceLast = null;
         this.pendingLookup = false;
         this.options = null;
+        this.ignoreNodes = (Array.isArray(ignoreNodes) && ignoreNodes.length > 0 ? ignoreNodes.join(',') : null);
 
         this.primaryTouchIdentifier = null;
         this.contextMenuChecking = false;
@@ -39,10 +40,10 @@ class Frontend {
     static create() {
         const initializationData = window.frontendInitializationData;
         const isNested = (initializationData !== null && typeof initializationData === 'object');
-        const {id, parentFrameId} = initializationData || {};
+        const {id, parentFrameId, ignoreNodes} = isNested ? initializationData : {};
 
         const popup = isNested ? new PopupProxy(id, parentFrameId) : PopupProxyHost.instance.createPopup(null);
-        const frontend = new Frontend(popup);
+        const frontend = new Frontend(popup, ignoreNodes);
         frontend.prepare();
         return frontend;
     }
@@ -337,9 +338,14 @@ class Frontend {
     }
 
     async searchTerms(textSource, focus) {
-        textSource.setEndOffset(this.options.scanning.length);
+        this.setTextSourceScanLength(textSource, this.options.scanning.length);
 
-        const {definitions, length} = await apiTermsFind(textSource.text());
+        const searchText = textSource.text();
+        if (searchText.length === 0) {
+            return;
+        }
+
+        const {definitions, length} = await apiTermsFind(searchText);
         if (definitions.length === 0) {
             return false;
         }
@@ -365,9 +371,14 @@ class Frontend {
     }
 
     async searchKanji(textSource, focus) {
-        textSource.setEndOffset(1);
+        this.setTextSourceScanLength(textSource, 1);
 
-        const definitions = await apiKanjiFind(textSource.text());
+        const searchText = textSource.text();
+        if (searchText.length === 0) {
+            return;
+        }
+
+        const definitions = await apiKanjiFind(searchText);
         if (definitions.length === 0) {
             return false;
         }
@@ -493,6 +504,67 @@ class Frontend {
         }
         return false;
     }
+
+    setTextSourceScanLength(textSource, length) {
+        textSource.setEndOffset(length);
+        if (this.ignoreNodes === null || !textSource.range) {
+            return;
+        }
+
+        length = textSource.text().length;
+        while (textSource.range && length > 0) {
+            const nodes = Frontend.getNodesInRange(textSource.range);
+            if (Frontend.isValidScanningNodeList(nodes, this.ignoreNodes)) {
+                break;
+            }
+            --length;
+            textSource.setEndOffset(length);
+        }
+    }
+
+    static getNodesInRange(range) {
+        const end = range.endContainer;
+        const nodes = [];
+        for (let node = range.startContainer; node !== null; node = Frontend.getNextNode(node)) {
+            nodes.push(node);
+            if (node === end) { break; }
+        }
+        return nodes;
+    }
+
+    static getNextNode(node) {
+        let next = node.firstChild;
+        if (next === null) {
+            while (true) {
+                next = node.nextSibling;
+                if (next !== null) { break; }
+
+                next = node.parentNode;
+                if (node === null) { break; }
+
+                node = next;
+            }
+        }
+        return next;
+    }
+
+    static isValidScanningNodeList(nodeList, selector) {
+        for (const node of nodeList) {
+            if (!Frontend.isValidScanningNode(node, selector)) {
+                return false;
+            }
+        }
+        return true;
+    }
+
+    static isValidScanningNode(node, selector) {
+        for (; node !== null; node = node.parentNode) {
+            if (node.nodeType === Node.ELEMENT_NODE) {
+                return !node.matches(selector);
+            }
+        }
+        return true;
+    }
 }
 
 window.yomichan_frontend = Frontend.create();
diff --git a/ext/fg/js/popup-nested.js b/ext/fg/js/popup-nested.js
index ad235cc6..e0376bb2 100644
--- a/ext/fg/js/popup-nested.js
+++ b/ext/fg/js/popup-nested.js
@@ -32,7 +32,9 @@ async function popupNestedInitialize(id, depth, parentFrameId) {
         return;
     }
 
-    window.frontendInitializationData = {id, depth, parentFrameId};
+    const ignoreNodes = options.scanning.enableOnPopupExpressions ? [] : [ '.expression', '.expression *' ];
+
+    window.frontendInitializationData = {id, depth, parentFrameId, ignoreNodes};
 
     const scriptSrcs = [
         '/fg/js/frontend-api-sender.js',