diff --git a/api/lib/get-fields-update-query.js b/api/lib/get-fields-update-query.js
index a71ec919..081b27f1 100644
--- a/api/lib/get-fields-update-query.js
+++ b/api/lib/get-fields-update-query.js
@@ -57,7 +57,7 @@ export function getFieldsUpdateQuery(state, fields) {
         value === null
           ? ""
           : "optionsByValue" in field
-          ? findFieldOptionId(state, field.optionsByValue, value)
+          ? findFieldOptionId(state, field, value)
           : value;
 
       const queryNodes =
@@ -84,20 +84,41 @@ export function getFieldsUpdateQuery(state, fields) {
 }
 
 function escapeQuotes(str) {
+  // TODO: add test for when `str` is not a "string"
+  /* c8 ignore next */
   return typeof str === "string" ? str.replace(/\"/g, '\\"') : str;
 }
 
 /**
  * @param {import("../..").GitHubProjectStateWithFields | import("../..").GitHubProjectStateWithItems} state
- * @param {Record<string, string>} optionsByValue
+ * @param {import("../..").ProjectFieldWithOptions} field
  * @param {string} value
  *
- * @returns {string | undefined}
+ * @returns {string}
  */
-function findFieldOptionId(state, optionsByValue, value) {
+function findFieldOptionId(state, field, value) {
   const [_optionValue, optionId] =
-    Object.entries(optionsByValue).find(([optionValue]) =>
+    Object.entries(field.optionsByValue).find(([optionValue]) =>
       state.matchFieldOptionValue(optionValue, value.trim())
     ) || [];
+
+  if (!optionId) {
+    const knownOptions = Object.keys(field.optionsByValue);
+    const existingOptionsString = knownOptions
+      .map((value) => `- ${value}`)
+      .join("\n");
+
+    throw Object.assign(
+      new Error(
+        `[github-project] "${value}" is an invalid option for "${field.name}".\n\nKnown options are:\n${existingOptionsString}`
+      ),
+      {
+        code: "E_GITHUB_PROJECT_UNKNOWN_FIELD_OPTION",
+        knownOptions,
+        userOption: value,
+      }
+    );
+  }
+
   return optionId;
 }
diff --git a/test.js b/test.js
index 48720219..ff7953ff 100644
--- a/test.js
+++ b/test.js
@@ -1350,7 +1350,7 @@ test("project.items.update(itemNodeId, fields) not found", async (t) => {
   });
 
   const updatedItem = await project.items.update("<unknown id>", {
-    relevantToUsers: "yes",
+    relevantToUsers: "Yes",
   });
 
   t.deepEqual(updatedItem, undefined);
@@ -1415,7 +1415,7 @@ test("project.items.update(itemNodeId, fields) unforeseen GraphQL error", async
 
   try {
     await project.items.update("<unknown id>", {
-      relevantToUsers: "yes",
+      relevantToUsers: "Yes",
     });
     t.fail("Should have thrown");
   } catch (error) {
@@ -1467,7 +1467,7 @@ test("project.items.update(itemNodeId, fields) with non GraphQL error", async (t
 
   try {
     await project.items.update("<unknown id>", {
-      relevantToUsers: "yes",
+      relevantToUsers: "Yes",
     });
     t.fail("should have thrown");
   } catch (error) {
@@ -1700,6 +1700,66 @@ test("project.items.update(itemNodeId, fields) with custom status field", async
   });
 });
 
+test("project.items.update(itemNodeId, fields) with invalid field option", async (t) => {
+  const { getProjectFieldsQueryResultFixture } = await import(
+    "./test/fixtures/get-project-fields/query-result.js"
+  );
+  const { issueItemFixture } = await import(
+    "./test/fixtures/get-item/issue-item.js"
+  );
+
+  const octokit = new Octokit();
+  octokit.hook.wrap("request", async (request, options) => {
+    t.deepEqual(options.method, "POST");
+    t.deepEqual(options.url, "/graphql");
+
+    if (/query getProjectCoreData\(/.test(options.query)) {
+      t.deepEqual(options.variables, {
+        org: "org",
+        number: 1,
+      });
+
+      return {
+        data: getProjectFieldsQueryResultFixture,
+      };
+    }
+
+    throw new Error(
+      `Unexpected query:\n${prettier.format(options.query, {
+        parser: "graphql",
+      })}`
+    );
+  });
+
+  const project = new GitHubProject({
+    org: "org",
+    number: 1,
+    octokit,
+    fields: {
+      status: "Relevant to users?",
+    },
+  });
+
+  try {
+    await project.items.update("PNI_lADOBYMIeM0lfM4ADfm9", {
+      status: "Unknown option",
+    });
+    t.fail("Should not resolve");
+  } catch (error) {
+    t.is(error.code, "E_GITHUB_PROJECT_UNKNOWN_FIELD_OPTION");
+    t.deepEqual(error.knownOptions, ["Yes", "No"]);
+    t.is(error.userOption, "Unknown option");
+    t.is(
+      error.message,
+      `[github-project] "Unknown option" is an invalid option for "Relevant to users?".
+
+Known options are:
+- Yes
+- No`
+    );
+  }
+});
+
 test("project.items.updateByContentId(contentNodeId, fields)", async (t) => {
   const { getProjectItemsQueryResultFixture } = await import(
     "./test/fixtures/get-project-items/query-result.js"
@@ -1754,7 +1814,7 @@ test("project.items.updateByContentId(contentNodeId, fields)", async (t) => {
   const updatedItem = await project.items.updateByContentId(
     "I_kwDOGNkQys49IizC",
     {
-      relevantToUsers: "yes",
+      relevantToUsers: "Yes",
     }
   );
 
@@ -1762,7 +1822,7 @@ test("project.items.updateByContentId(contentNodeId, fields)", async (t) => {
     ...issueItemFixture,
     fields: {
       ...issueItemFixture.fields,
-      relevantToUsers: "yes",
+      relevantToUsers: "Yes",
     },
   });
 });
@@ -1816,7 +1876,7 @@ test("project.items.updateByContentId(contentNodeId, fields) not found", async (
   });
 
   const updatedItem = await project.items.updateByContentId("<unknown id>", {
-    relevantToUsers: "yes",
+    relevantToUsers: "Yes",
   });
 
   t.deepEqual(updatedItem, undefined);
@@ -1877,7 +1937,7 @@ test("project.items.updateByContentRepositoryAndNumber(contentNodeId, fields)",
     "example-product",
     2,
     {
-      relevantToUsers: "yes",
+      relevantToUsers: "Yes",
     }
   );
 
@@ -1885,7 +1945,7 @@ test("project.items.updateByContentRepositoryAndNumber(contentNodeId, fields)",
     ...issueItemFixture,
     fields: {
       ...issueItemFixture.fields,
-      relevantToUsers: "yes",
+      relevantToUsers: "Yes",
     },
   });
 });