diff --git a/.changeset/gentle-moles-jump.md b/.changeset/gentle-moles-jump.md
new file mode 100644
index 0000000..d13ff89
--- /dev/null
+++ b/.changeset/gentle-moles-jump.md
@@ -0,0 +1,5 @@
+---
+"@guardian/cql": patch
+---
+
+Fix `queryChange`'s serialised `queryStr` dropping quotes from a plain phrase containing a reserved character (`:`, `(`, `)`, or `"`) with no whitespace, e.g. `"hello:world"`. Previously only whitespace triggered re-quoting for plain phrases, while chip keys/values already correctly checked reserved characters too — the two now use the same predicate (`shouldQuoteFieldValue`). Without this fix, a quoted phrase containing a colon is silently corrupted into an unquoted string, which then gets mis-parsed as a `key:value` chip the next time it's read.
diff --git a/lib/cql/src/lang/interpreter.spec.ts b/lib/cql/src/lang/interpreter.spec.ts
index 9389751..bd7045e 100644
--- a/lib/cql/src/lang/interpreter.spec.ts
+++ b/lib/cql/src/lang/interpreter.spec.ts
@@ -27,6 +27,33 @@ describe("interpreter", () => {
     expect(str).toBe(queryStr);
   });
 
+  it("should quote a plain string containing a reserved char (colon)", () => {
+    const queryStr = `"hello:world"`;
+    const query = parser(queryStr).queryAst!;
+
+    const str = cqlQueryStrFromQueryAst(query);
+
+    expect(str).toBe(queryStr);
+  });
+
+  it("should quote a plain string containing a reserved char (parens)", () => {
+    const queryStr = `"(parenthetical)"`;
+    const query = parser(queryStr).queryAst!;
+
+    const str = cqlQueryStrFromQueryAst(query);
+
+    expect(str).toBe(queryStr);
+  });
+
+  it("should not quote a plain string with no reserved chars or whitespace", () => {
+    const queryStr = `hello`;
+    const query = parser(queryStr).queryAst!;
+
+    const str = cqlQueryStrFromQueryAst(query);
+
+    expect(str).toBe(queryStr);
+  });
+
   it("should escape reserved characters in chip keys and values", () => {
     const queryStr = `key:"\\"value\\""`;
     const query = parser(queryStr).queryAst!;
diff --git a/lib/cql/src/lang/interpreter.ts b/lib/cql/src/lang/interpreter.ts
index 92fa1ab..bcc6070 100644
--- a/lib/cql/src/lang/interpreter.ts
+++ b/lib/cql/src/lang/interpreter.ts
@@ -1,5 +1,5 @@
 import { CqlBinary, CqlExpr, CqlField, CqlQuery } from "./ast";
-import { hasWhitespace, shouldQuoteFieldValue } from "./utils";
+import { shouldQuoteFieldValue } from "./utils";
 
 export const cqlQueryStrFromQueryAst = (query: CqlQuery): string => {
   const { content } = query;
@@ -17,7 +17,7 @@ const strFromExpr = (queryExpr: CqlExpr): string | undefined => {
   const renderedContent = (() => {
     switch (content.type) {
       case "CqlStr":
-        return hasWhitespace(content.searchExpr)
+        return shouldQuoteFieldValue(content.searchExpr)
           ? `"${content.searchExpr}"`
           : content.searchExpr;
       case "CqlGroup":