diff --git a/src/scripting_api/aform.js b/src/scripting_api/aform.js
index c91d72786f07f..747f503740576 100644
--- a/src/scripting_api/aform.js
+++ b/src/scripting_api/aform.js
@@ -486,15 +486,15 @@ class AForm {
     ]);
 
     function _checkValidity(_value, _cMask) {
-      for (let i = 0, ii = value.length; i < ii; i++) {
-        const mask = _cMask.charAt(i);
-        const char = _value.charAt(i);
-        const checker = checkers.get(mask);
+      for (let i = 0, ii = _value.length; i < ii; i++) {
+        const maskChar = _cMask.charAt(i);
+        const valueChar = _value.charAt(i);
+        const checker = checkers.get(maskChar);
         if (checker) {
-          if (!checker(char)) {
+          if (!checker(valueChar)) {
             return false;
           }
-        } else if (mask !== char) {
+        } else if (maskChar !== valueChar) {
           return false;
         }
       }
@@ -564,7 +564,7 @@ class AForm {
           event.change.length +
           event.selStart -
           event.selEnd;
-        if (finalLen >= 8) {
+        if (finalLen > 8 || event.value[0] === "(") {
           formatStr = "(999) 999-9999";
         } else {
           formatStr = "999-9999";
diff --git a/src/scripting_api/event.js b/src/scripting_api/event.js
index a06fb0220b024..5b5bb082e75bc 100644
--- a/src/scripting_api/event.js
+++ b/src/scripting_api/event.js
@@ -47,11 +47,32 @@ class EventDispatcher {
     this._document.obj._eventDispatcher = this;
   }
 
+  /*
+   * Take an event object and reconstruct what we think the result will be once
+   * the change is applied, so we can validate against it and cancel the event
+   * if need be
+   *
+   * TODO: Given the event info we currently have, we can't determine where in
+   * the value a single-character insertion/deletion happened.  For now we just
+   * assume they happen at the end of the string, which is by far the most
+   * common case, but this leaves some edge cases, see issue #14307.
+   */
   mergeChange(event) {
     let value = event.value;
     if (typeof value !== "string") {
       value = value.toString();
     }
+    // If there was no selection, it's a single-character change
+    if (event.selStart === -1 && event.selEnd === -1) {
+      if (event.change === "") {
+        // Empty change indicates a deletion
+        return value.slice(0, -1);
+      }
+      // Otherwise, assume it's an append
+      return value + event.change;
+    }
+
+    // Otherwise, splice in the change to replace the selection
     const prefix =
       event.selStart >= 0 ? value.substring(0, event.selStart) : "";
     const postfix =
diff --git a/test/unit/scripting_spec.js b/test/unit/scripting_spec.js
index c6236761b6023..46fe7d5f5dac3 100644
--- a/test/unit/scripting_spec.js
+++ b/test/unit/scripting_spec.js
@@ -361,15 +361,15 @@ describe("Scripting", function () {
         name: "Keystroke",
         willCommit: false,
         change: "o",
-        selStart: 4,
-        selEnd: 4,
+        selStart: -1,
+        selEnd: -1,
       });
 
       expect(send_queue.has(refId)).toEqual(true);
       expect(send_queue.get(refId)).toEqual({
         id: refId,
         value: "hell",
-        selRange: [4, 4],
+        selRange: [-1, -1],
       });
     });
 
@@ -398,8 +398,8 @@ describe("Scripting", function () {
         name: "Keystroke",
         willCommit: false,
         change: "o",
-        selStart: 4,
-        selEnd: 4,
+        selStart: -1,
+        selEnd: -1,
       });
 
       expect(send_queue.has(refId)).toEqual(true);
@@ -1119,8 +1119,8 @@ describe("Scripting", function () {
           change: "3",
           name: "Keystroke",
           willCommit: false,
-          selStart: 0,
-          selEnd: 0,
+          selStart: -1,
+          selEnd: -1,
         });
         expect(send_queue.has(refId)).toEqual(false);
 
@@ -1130,8 +1130,8 @@ describe("Scripting", function () {
           change: "F",
           name: "Keystroke",
           willCommit: false,
-          selStart: 1,
-          selEnd: 1,
+          selStart: -1,
+          selEnd: -1,
         });
         expect(send_queue.has(refId)).toEqual(false);
 
@@ -1141,8 +1141,8 @@ describe("Scripting", function () {
           change: "?",
           name: "Keystroke",
           willCommit: false,
-          selStart: 2,
-          selEnd: 2,
+          selStart: -1,
+          selEnd: -1,
         });
         expect(send_queue.has(refId)).toEqual(false);
 
@@ -1152,14 +1152,14 @@ describe("Scripting", function () {
           change: "@",
           name: "Keystroke",
           willCommit: false,
-          selStart: 3,
-          selEnd: 3,
+          selStart: -1,
+          selEnd: -1,
         });
         expect(send_queue.has(refId)).toEqual(true);
         expect(send_queue.get(refId)).toEqual({
           id: refId,
           value: "3F?",
-          selRange: [3, 3],
+          selRange: [-1, -1],
         });
 
         send_queue.delete(refId);
@@ -1169,7 +1169,7 @@ describe("Scripting", function () {
           change: "0",
           name: "Keystroke",
           willCommit: true,
-          selStart: 3,
+          selStart: -1,
           selEnd: 3,
         });
         expect(send_queue.has(refId)).toEqual(false);