diff --git a/CHANGELOG.md b/CHANGELOG.md
index bd51cb89cb..bb40ada291 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,10 @@ See the [releases page](https://github.com/github/codeql-action/releases) for th
 
 Note that the only difference between `v2` and `v3` of the CodeQL Action is the node version they support, with `v3` running on node 20 while we continue to release `v2` to support running on node 16. For example `3.22.11` was the first `v3` release and is functionally identical to `2.22.11`. This approach ensures an easy way to track exactly which features are included in different versions, indicated by the minor and patch version numbers.
 
+## 3.26.3 - 19 Aug 2024
+
+- Fix an issue where the CodeQL Action could not write diagnostic messages on Windows. This issue did not impact analysis quality. [#2430](https://github.com/github/codeql-action/pull/2430)
+
 ## 3.26.2 - 14 Aug 2024
 
 - Update default CodeQL bundle version to 2.18.2. [#2417](https://github.com/github/codeql-action/pull/2417)
diff --git a/lib/diagnostics.js b/lib/diagnostics.js
index 4743424e96..a8d3ccd055 100644
--- a/lib/diagnostics.js
+++ b/lib/diagnostics.js
@@ -67,7 +67,9 @@ function writeDiagnostic(config, language, diagnostic) {
     try {
         // Create the directory if it doesn't exist yet.
         (0, fs_1.mkdirSync)(diagnosticsPath, { recursive: true });
-        const jsonPath = path_1.default.resolve(diagnosticsPath, `codeql-action-${diagnostic.timestamp}.json`);
+        const jsonPath = path_1.default.resolve(diagnosticsPath, 
+        // Remove colons from the timestamp as these are not allowed in Windows filenames.
+        `codeql-action-${diagnostic.timestamp.replaceAll(":", "")}.json`);
         (0, fs_1.writeFileSync)(jsonPath, JSON.stringify(diagnostic));
     }
     catch (err) {
diff --git a/lib/diagnostics.js.map b/lib/diagnostics.js.map
index bee7607358..ad057d1f55 100644
--- a/lib/diagnostics.js.map
+++ b/lib/diagnostics.js.map
@@ -1 +1 @@
-{"version":3,"file":"diagnostics.js","sourceRoot":"","sources":["../src/diagnostics.ts"],"names":[],"mappings":";;;;;AA4EA,wCAUC;AAUD,sCAqBC;AAyCD,0DAYC;AAGD,4CAYC;AAzLD,2BAA0D;AAC1D,gDAAwB;AAIxB,uCAA6C;AAC7C,iCAA+C;AA2D/C,qEAAqE;AACrE,IAAI,oBAAoB,GAA0B,EAAE,CAAC;AAErD;;;;;;;GAOG;AACH,SAAgB,cAAc,CAC5B,EAAU,EACV,IAAY,EACZ,OAA+C,SAAS;IAExD,OAAO;QACL,GAAG,IAAI;QACP,SAAS,EAAE,IAAI,EAAE,SAAS,IAAI,IAAI,IAAI,EAAE,CAAC,WAAW,EAAE;QACtD,MAAM,EAAE,EAAE,GAAG,IAAI,EAAE,MAAM,EAAE,EAAE,EAAE,IAAI,EAAE;KACtC,CAAC;AACJ,CAAC;AAED;;;;;;;GAOG;AACH,SAAgB,aAAa,CAC3B,MAAc,EACd,QAAkB,EAClB,UAA6B;IAE7B,MAAM,MAAM,GAAG,IAAA,0BAAgB,GAAE,CAAC;IAClC,MAAM,YAAY,GAAG,QAAQ;QAC3B,CAAC,CAAC,IAAA,4BAAqB,EAAC,MAAM,EAAE,QAAQ,CAAC;QACzC,CAAC,CAAC,MAAM,CAAC,UAAU,CAAC;IAEtB,2FAA2F;IAC3F,qDAAqD;IACrD,IAAI,IAAA,eAAU,EAAC,YAAY,CAAC,EAAE,CAAC;QAC7B,eAAe,CAAC,MAAM,EAAE,QAAQ,EAAE,UAAU,CAAC,CAAC;IAChD,CAAC;SAAM,CAAC;QACN,MAAM,CAAC,KAAK,CACV,4BAA4B,QAAQ,yBAAyB,YAAY,sBAAsB,CAChG,CAAC;QAEF,oBAAoB,CAAC,IAAI,CAAC,EAAE,UAAU,EAAE,QAAQ,EAAE,CAAC,CAAC;IACtD,CAAC;AACH,CAAC;AAED;;;;;;GAMG;AACH,SAAS,eAAe,CACtB,MAAc,EACd,QAA8B,EAC9B,UAA6B;IAE7B,MAAM,MAAM,GAAG,IAAA,0BAAgB,GAAE,CAAC;IAClC,MAAM,YAAY,GAAG,QAAQ;QAC3B,CAAC,CAAC,IAAA,4BAAqB,EAAC,MAAM,EAAE,QAAQ,CAAC;QACzC,CAAC,CAAC,MAAM,CAAC,UAAU,CAAC;IACtB,MAAM,eAAe,GAAG,cAAI,CAAC,OAAO,CAClC,YAAY,EACZ,YAAY,EACZ,eAAe,CAChB,CAAC;IAEF,IAAI,CAAC;QACH,gDAAgD;QAChD,IAAA,cAAS,EAAC,eAAe,EAAE,EAAE,SAAS,EAAE,IAAI,EAAE,CAAC,CAAC;QAEhD,MAAM,QAAQ,GAAG,cAAI,CAAC,OAAO,CAC3B,eAAe,EACf,iBAAiB,UAAU,CAAC,SAAS,OAAO,CAC7C,CAAC;QAEF,IAAA,kBAAa,EAAC,QAAQ,EAAE,IAAI,CAAC,SAAS,CAAC,UAAU,CAAC,CAAC,CAAC;IACtD,CAAC;IAAC,OAAO,GAAG,EAAE,CAAC;QACb,MAAM,CAAC,OAAO,CAAC,mDAAmD,GAAG,EAAE,CAAC,CAAC;QACzE,MAAM,CAAC,KAAK,CAAC,IAAI,CAAC,SAAS,CAAC,UAAU,CAAC,CAAC,CAAC;IAC3C,CAAC;AACH,CAAC;AAED,2EAA2E;AAC3E,SAAgB,uBAAuB;IACrC,MAAM,MAAM,GAAG,IAAA,0BAAgB,GAAE,CAAC;IAClC,MAAM,GAAG,GAAG,oBAAoB,CAAC,MAAM,CAAC;IACxC,IAAI,GAAG,GAAG,CAAC,EAAE,CAAC;QACZ,MAAM,CAAC,OAAO,CACZ,GAAG,GAAG,kGAAkG,CACzG,CAAC;QAEF,KAAK,MAAM,SAAS,IAAI,oBAAoB,EAAE,CAAC;YAC7C,MAAM,CAAC,KAAK,CAAC,IAAI,CAAC,SAAS,CAAC,SAAS,CAAC,UAAU,CAAC,CAAC,CAAC;QACrD,CAAC;IACH,CAAC;AACH,CAAC;AAED,gDAAgD;AAChD,SAAgB,gBAAgB,CAAC,MAAc;IAC7C,MAAM,MAAM,GAAG,IAAA,0BAAgB,GAAE,CAAC;IAClC,MAAM,CAAC,KAAK,CACV,WAAW,oBAAoB,CAAC,MAAM,6BAA6B,CACpE,CAAC;IAEF,KAAK,MAAM,SAAS,IAAI,oBAAoB,EAAE,CAAC;QAC7C,eAAe,CAAC,MAAM,EAAE,SAAS,CAAC,QAAQ,EAAE,SAAS,CAAC,UAAU,CAAC,CAAC;IACpE,CAAC;IAED,yCAAyC;IACzC,oBAAoB,GAAG,EAAE,CAAC;AAC5B,CAAC"}
\ No newline at end of file
+{"version":3,"file":"diagnostics.js","sourceRoot":"","sources":["../src/diagnostics.ts"],"names":[],"mappings":";;;;;AA4EA,wCAUC;AAUD,sCAqBC;AA0CD,0DAYC;AAGD,4CAYC;AA1LD,2BAA0D;AAC1D,gDAAwB;AAIxB,uCAA6C;AAC7C,iCAA+C;AA2D/C,qEAAqE;AACrE,IAAI,oBAAoB,GAA0B,EAAE,CAAC;AAErD;;;;;;;GAOG;AACH,SAAgB,cAAc,CAC5B,EAAU,EACV,IAAY,EACZ,OAA+C,SAAS;IAExD,OAAO;QACL,GAAG,IAAI;QACP,SAAS,EAAE,IAAI,EAAE,SAAS,IAAI,IAAI,IAAI,EAAE,CAAC,WAAW,EAAE;QACtD,MAAM,EAAE,EAAE,GAAG,IAAI,EAAE,MAAM,EAAE,EAAE,EAAE,IAAI,EAAE;KACtC,CAAC;AACJ,CAAC;AAED;;;;;;;GAOG;AACH,SAAgB,aAAa,CAC3B,MAAc,EACd,QAAkB,EAClB,UAA6B;IAE7B,MAAM,MAAM,GAAG,IAAA,0BAAgB,GAAE,CAAC;IAClC,MAAM,YAAY,GAAG,QAAQ;QAC3B,CAAC,CAAC,IAAA,4BAAqB,EAAC,MAAM,EAAE,QAAQ,CAAC;QACzC,CAAC,CAAC,MAAM,CAAC,UAAU,CAAC;IAEtB,2FAA2F;IAC3F,qDAAqD;IACrD,IAAI,IAAA,eAAU,EAAC,YAAY,CAAC,EAAE,CAAC;QAC7B,eAAe,CAAC,MAAM,EAAE,QAAQ,EAAE,UAAU,CAAC,CAAC;IAChD,CAAC;SAAM,CAAC;QACN,MAAM,CAAC,KAAK,CACV,4BAA4B,QAAQ,yBAAyB,YAAY,sBAAsB,CAChG,CAAC;QAEF,oBAAoB,CAAC,IAAI,CAAC,EAAE,UAAU,EAAE,QAAQ,EAAE,CAAC,CAAC;IACtD,CAAC;AACH,CAAC;AAED;;;;;;GAMG;AACH,SAAS,eAAe,CACtB,MAAc,EACd,QAA8B,EAC9B,UAA6B;IAE7B,MAAM,MAAM,GAAG,IAAA,0BAAgB,GAAE,CAAC;IAClC,MAAM,YAAY,GAAG,QAAQ;QAC3B,CAAC,CAAC,IAAA,4BAAqB,EAAC,MAAM,EAAE,QAAQ,CAAC;QACzC,CAAC,CAAC,MAAM,CAAC,UAAU,CAAC;IACtB,MAAM,eAAe,GAAG,cAAI,CAAC,OAAO,CAClC,YAAY,EACZ,YAAY,EACZ,eAAe,CAChB,CAAC;IAEF,IAAI,CAAC;QACH,gDAAgD;QAChD,IAAA,cAAS,EAAC,eAAe,EAAE,EAAE,SAAS,EAAE,IAAI,EAAE,CAAC,CAAC;QAEhD,MAAM,QAAQ,GAAG,cAAI,CAAC,OAAO,CAC3B,eAAe;QACf,kFAAkF;QAClF,iBAAiB,UAAU,CAAC,SAAS,CAAC,UAAU,CAAC,GAAG,EAAE,EAAE,CAAC,OAAO,CACjE,CAAC;QAEF,IAAA,kBAAa,EAAC,QAAQ,EAAE,IAAI,CAAC,SAAS,CAAC,UAAU,CAAC,CAAC,CAAC;IACtD,CAAC;IAAC,OAAO,GAAG,EAAE,CAAC;QACb,MAAM,CAAC,OAAO,CAAC,mDAAmD,GAAG,EAAE,CAAC,CAAC;QACzE,MAAM,CAAC,KAAK,CAAC,IAAI,CAAC,SAAS,CAAC,UAAU,CAAC,CAAC,CAAC;IAC3C,CAAC;AACH,CAAC;AAED,2EAA2E;AAC3E,SAAgB,uBAAuB;IACrC,MAAM,MAAM,GAAG,IAAA,0BAAgB,GAAE,CAAC;IAClC,MAAM,GAAG,GAAG,oBAAoB,CAAC,MAAM,CAAC;IACxC,IAAI,GAAG,GAAG,CAAC,EAAE,CAAC;QACZ,MAAM,CAAC,OAAO,CACZ,GAAG,GAAG,kGAAkG,CACzG,CAAC;QAEF,KAAK,MAAM,SAAS,IAAI,oBAAoB,EAAE,CAAC;YAC7C,MAAM,CAAC,KAAK,CAAC,IAAI,CAAC,SAAS,CAAC,SAAS,CAAC,UAAU,CAAC,CAAC,CAAC;QACrD,CAAC;IACH,CAAC;AACH,CAAC;AAED,gDAAgD;AAChD,SAAgB,gBAAgB,CAAC,MAAc;IAC7C,MAAM,MAAM,GAAG,IAAA,0BAAgB,GAAE,CAAC;IAClC,MAAM,CAAC,KAAK,CACV,WAAW,oBAAoB,CAAC,MAAM,6BAA6B,CACpE,CAAC;IAEF,KAAK,MAAM,SAAS,IAAI,oBAAoB,EAAE,CAAC;QAC7C,eAAe,CAAC,MAAM,EAAE,SAAS,CAAC,QAAQ,EAAE,SAAS,CAAC,UAAU,CAAC,CAAC;IACpE,CAAC;IAED,yCAAyC;IACzC,oBAAoB,GAAG,EAAE,CAAC;AAC5B,CAAC"}
\ No newline at end of file
diff --git a/node_modules/.package-lock.json b/node_modules/.package-lock.json
index aaded43f84..ae9e2d9e97 100644
--- a/node_modules/.package-lock.json
+++ b/node_modules/.package-lock.json
@@ -1,6 +1,6 @@
 {
   "name": "codeql",
-  "version": "3.26.2",
+  "version": "3.26.3",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
diff --git a/package-lock.json b/package-lock.json
index 7c2c04f5d7..b9686c7299 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,12 +1,12 @@
 {
   "name": "codeql",
-  "version": "3.26.2",
+  "version": "3.26.3",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "codeql",
-      "version": "3.26.2",
+      "version": "3.26.3",
       "license": "MIT",
       "dependencies": {
         "@actions/artifact": "^1.1.2",
diff --git a/package.json b/package.json
index 4d818ce535..bcd2fb27a8 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "codeql",
-  "version": "3.26.2",
+  "version": "3.26.3",
   "private": true,
   "description": "CodeQL action",
   "scripts": {
diff --git a/src/diagnostics.ts b/src/diagnostics.ts
index b8c840c3e1..b3d18b23cb 100644
--- a/src/diagnostics.ts
+++ b/src/diagnostics.ts
@@ -145,7 +145,8 @@ function writeDiagnostic(
 
     const jsonPath = path.resolve(
       diagnosticsPath,
-      `codeql-action-${diagnostic.timestamp}.json`,
+      // Remove colons from the timestamp as these are not allowed in Windows filenames.
+      `codeql-action-${diagnostic.timestamp.replaceAll(":", "")}.json`,
     );
 
     writeFileSync(jsonPath, JSON.stringify(diagnostic));