diff --git a/tracdap-api/packages/web/api_builder.js b/tracdap-api/packages/web/api_builder.js
index de5762bcd..9c4a1456c 100644
--- a/tracdap-api/packages/web/api_builder.js
+++ b/tracdap-api/packages/web/api_builder.js
@@ -35,7 +35,7 @@ const pbjsArgs = [
     "--wrap", "./wrapper.js",
     "--root", "tracdap",
     "--force-number",               // Use native JavaScript numbers for numeric types
-    "--null-defaults",              // Set optional fields to null if they are not present
+    "--null-semantics",             // Make nullability in TS / JSDoc respect optional semantics
     "--path", './build',
     "--out", jsOutFile
 ];
diff --git a/tracdap-api/packages/web/package-lock.json b/tracdap-api/packages/web/package-lock.json
index dd4deddbf..19f57f11c 100644
--- a/tracdap-api/packages/web/package-lock.json
+++ b/tracdap-api/packages/web/package-lock.json
@@ -10,13 +10,13 @@
       "license": "Apache-2.0",
       "dependencies": {
         "grpc-web": "~1.5.0",
-        "protobufjs": "~7.3.2"
+        "protobufjs": "~7.3.3"
       },
       "devDependencies": {
         "license-checker-rseidelsohn": "~4.1.1",
         "node-fetch": "^3.3.2",
         "owasp-dependency-check": "~0.0.23",
-        "protobufjs-cli": "~1.1.2"
+        "protobufjs-cli": "~1.1.3"
       }
     },
     "node_modules/@babel/parser": {
@@ -1130,11 +1130,10 @@
       }
     },
     "node_modules/protobufjs": {
-      "version": "7.3.2",
-      "resolved": "https://registry.npmjs.org/protobufjs/-/protobufjs-7.3.2.tgz",
-      "integrity": "sha512-RXyHaACeqXeqAKGLDl68rQKbmObRsTIn4TYVUUug1KfS47YWCo5MacGITEryugIgZqORCvJWEk4l449POg5Txg==",
+      "version": "7.3.3",
+      "resolved": "https://registry.npmjs.org/protobufjs/-/protobufjs-7.3.3.tgz",
+      "integrity": "sha512-HaYi2CVjiPoBR1d2zTVKVHXr9IUnpJizCjUu19vxdD3B8o4z+vfOHpIEB1358w8nv8dfUNEfDHFvMsH7QlLt/Q==",
       "hasInstallScript": true,
-      "license": "BSD-3-Clause",
       "dependencies": {
         "@protobufjs/aspromise": "^1.1.2",
         "@protobufjs/base64": "^1.1.2",
@@ -1154,9 +1153,9 @@
       }
     },
     "node_modules/protobufjs-cli": {
-      "version": "1.1.2",
-      "resolved": "https://registry.npmjs.org/protobufjs-cli/-/protobufjs-cli-1.1.2.tgz",
-      "integrity": "sha512-8ivXWxT39gZN4mm4ArQyJrRgnIwZqffBWoLDsE21TmMcKI3XwJMV4lEF2WU02C4JAtgYYc2SfJIltelD8to35g==",
+      "version": "1.1.3",
+      "resolved": "https://registry.npmjs.org/protobufjs-cli/-/protobufjs-cli-1.1.3.tgz",
+      "integrity": "sha512-MqD10lqF+FMsOayFiNOdOGNlXc4iKDCf0ZQPkPR+gizYh9gqUeGTWulABUCdI+N67w5RfJ6xhgX4J8pa8qmMXQ==",
       "dev": true,
       "dependencies": {
         "chalk": "^4.0.0",
@@ -2453,9 +2452,9 @@
       "dev": true
     },
     "protobufjs": {
-      "version": "7.3.2",
-      "resolved": "https://registry.npmjs.org/protobufjs/-/protobufjs-7.3.2.tgz",
-      "integrity": "sha512-RXyHaACeqXeqAKGLDl68rQKbmObRsTIn4TYVUUug1KfS47YWCo5MacGITEryugIgZqORCvJWEk4l449POg5Txg==",
+      "version": "7.3.3",
+      "resolved": "https://registry.npmjs.org/protobufjs/-/protobufjs-7.3.3.tgz",
+      "integrity": "sha512-HaYi2CVjiPoBR1d2zTVKVHXr9IUnpJizCjUu19vxdD3B8o4z+vfOHpIEB1358w8nv8dfUNEfDHFvMsH7QlLt/Q==",
       "requires": {
         "@protobufjs/aspromise": "^1.1.2",
         "@protobufjs/base64": "^1.1.2",
@@ -2472,9 +2471,9 @@
       }
     },
     "protobufjs-cli": {
-      "version": "1.1.2",
-      "resolved": "https://registry.npmjs.org/protobufjs-cli/-/protobufjs-cli-1.1.2.tgz",
-      "integrity": "sha512-8ivXWxT39gZN4mm4ArQyJrRgnIwZqffBWoLDsE21TmMcKI3XwJMV4lEF2WU02C4JAtgYYc2SfJIltelD8to35g==",
+      "version": "1.1.3",
+      "resolved": "https://registry.npmjs.org/protobufjs-cli/-/protobufjs-cli-1.1.3.tgz",
+      "integrity": "sha512-MqD10lqF+FMsOayFiNOdOGNlXc4iKDCf0ZQPkPR+gizYh9gqUeGTWulABUCdI+N67w5RfJ6xhgX4J8pa8qmMXQ==",
       "dev": true,
       "requires": {
         "chalk": "^4.0.0",
diff --git a/tracdap-api/packages/web/package.json b/tracdap-api/packages/web/package.json
index 264445fc3..95561dd28 100644
--- a/tracdap-api/packages/web/package.json
+++ b/tracdap-api/packages/web/package.json
@@ -23,10 +23,10 @@
   "main": "tracdap.js",
   "dependencies": {
     "grpc-web": "~1.5.0",
-    "protobufjs": "~7.3.2"
+    "protobufjs": "~7.3.3"
   },
   "devDependencies": {
-    "protobufjs-cli": "~1.1.2",
+    "protobufjs-cli": "~1.1.3",
     "license-checker-rseidelsohn": "~4.1.1",
     "owasp-dependency-check": "~0.0.23",
     "node-fetch": "^3.3.2"