diff --git a/.chronus/changes/main-2024-5-13-14-52-31.md b/.chronus/changes/main-2024-5-13-14-52-31.md
new file mode 100644
index 0000000000..e5fa0ec174
--- /dev/null
+++ b/.chronus/changes/main-2024-5-13-14-52-31.md
@@ -0,0 +1,8 @@
+---
+# Change versionKind to one of: internal, fix, dependencies, feature, deprecation, breaking
+changeKind: fix
+packages:
+  - "@typespec/openapi3"
+---
+
+Emit diagnostic when an invalid type is used as a property instead of crashing.
diff --git a/packages/openapi3/src/lib.ts b/packages/openapi3/src/lib.ts
index 8b45badd1c..64ef47e267 100644
--- a/packages/openapi3/src/lib.ts
+++ b/packages/openapi3/src/lib.ts
@@ -245,6 +245,12 @@ export const libDef = {
         default: paramMessage`Status code range '${"start"} to '${"end"}' is not supported. OpenAPI 3.0 can only represent range 1XX, 2XX, 3XX, 4XX and 5XX. Example: \`@minValue(400) @maxValue(499)\` for 4XX.`,
       },
     },
+    "invalid-model-property": {
+      severity: "error",
+      messages: {
+        default: paramMessage`'${"type"}' cannot be specified as a model property.`,
+      },
+    },
     "unsupported-auth": {
       severity: "warning",
       messages: {
diff --git a/packages/openapi3/src/schema-emitter.ts b/packages/openapi3/src/schema-emitter.ts
index 44f10ae4a5..3e05cd9978 100644
--- a/packages/openapi3/src/schema-emitter.ts
+++ b/packages/openapi3/src/schema-emitter.ts
@@ -351,7 +351,14 @@ export class OpenAPI3SchemaEmitter extends TypeEmitter<
     });
 
     if (refSchema.kind !== "code") {
-      throw new Error("Unexpected non-code result from emit reference");
+      reportDiagnostic(program, {
+        code: "invalid-model-property",
+        format: {
+          type: prop.type.kind,
+        },
+        target: prop,
+      });
+      return {};
     }
 
     const isRef = refSchema.value instanceof Placeholder || "$ref" in refSchema.value;