diff --git a/packages/groq-builder/src/commands/conditional$.test.ts b/packages/groq-builder/src/commands/conditional$.test.ts
index 7c6b07a..b866f3a 100644
--- a/packages/groq-builder/src/commands/conditional$.test.ts
+++ b/packages/groq-builder/src/commands/conditional$.test.ts
@@ -25,6 +25,7 @@ describe("conditional$", () => {
         msrp: true,
       },
     });
+
     it("we should be able to extract the intersection of projection types", () => {
       expectType<
         Simplify<ExtractConditionalProjectionTypes<typeof conditionalResult>>
diff --git a/packages/groq-builder/src/commands/conditional$.ts b/packages/groq-builder/src/commands/conditional$.ts
index a075ab1..08c8c67 100644
--- a/packages/groq-builder/src/commands/conditional$.ts
+++ b/packages/groq-builder/src/commands/conditional$.ts
@@ -5,7 +5,6 @@ import {
   ConditionalKey,
   ConditionalProjectionMap,
   ExtractConditionalProjectionResults,
-  SpreadableConditionals,
 } from "./conditional-types";
 import { notNull } from "../types/utils";
 import { ParserFunction } from "../types/public-types";
@@ -19,23 +18,28 @@ declare module "../groq-builder" {
         ResultItem<TResult>,
         TRootConfig
       >,
-      TKey extends string = "[$]"
+      TKey extends string = "[$]",
+      TIsExhaustive extends boolean = false
     >(
       conditionalProjections: TConditionalProjections,
-      config?: ConditionalConfig<TKey>
+      config?: Partial<ConditionalConfig<TKey, TIsExhaustive>>
     ): ExtractConditionalProjectionResults<
       ResultItem<TResult>,
       TConditionalProjections,
-      TKey
+      ConditionalConfig<TKey, TIsExhaustive>
     >;
   }
 }
 
 GroqBuilder.implement({
-  conditional$<TCP extends object, TKey extends string>(
+  conditional$<
+    TCP extends object,
+    TKey extends string,
+    TIsExhaustive extends boolean
+  >(
     this: GroqBuilder,
     conditionalProjections: TCP,
-    config?: ConditionalConfig<TKey>
+    config?: Partial<ConditionalConfig<TKey, TIsExhaustive>>
   ) {
     const root = this.root;
     const allConditionalProjections = Object.entries(
@@ -58,20 +62,21 @@ GroqBuilder.implement({
       .filter(notNull);
     const conditionalParser = !parsers.length
       ? null
-      : createConditionalParserUnion(parsers);
+      : createConditionalParserUnion(parsers, config?.isExhaustive ?? false);
 
     const conditionalQuery = root.chain(query, conditionalParser);
-    const uniqueKey: ConditionalKey<TKey> = `[Conditional] ${
-      config?.key ?? ("[$]" as TKey)
-    }`;
-
+    const key = config?.key || ("[$]" as TKey);
+    const conditionalKey: ConditionalKey<TKey> = `[Conditional] ${key}`;
     return {
-      [uniqueKey]: conditionalQuery,
-    } as unknown as SpreadableConditionals<TKey, any>;
+      [conditionalKey]: conditionalQuery,
+    } as any;
   },
 });
 
-function createConditionalParserUnion(parsers: ParserFunction[]) {
+function createConditionalParserUnion(
+  parsers: ParserFunction[],
+  isExhaustive: boolean
+) {
   return function parserUnion(input: unknown) {
     for (const parser of parsers) {
       try {
@@ -82,6 +87,11 @@ function createConditionalParserUnion(parsers: ParserFunction[]) {
         // or if it errored due to not meeting the conditional check.
       }
     }
+    if (isExhaustive) {
+      throw new TypeError(
+        `The data did not match any of the ${parsers.length} conditional assertions`
+      );
+    }
     return {};
   };
 }
diff --git a/packages/groq-builder/src/commands/conditional-types.ts b/packages/groq-builder/src/commands/conditional-types.ts
index 3225a4c..e5e7aac 100644
--- a/packages/groq-builder/src/commands/conditional-types.ts
+++ b/packages/groq-builder/src/commands/conditional-types.ts
@@ -30,10 +30,10 @@ export type ConditionalExpression<TResultItem> = Tagged<string, TResultItem>;
 export type ExtractConditionalProjectionResults<
   TResultItem,
   TConditionalProjectionMap extends ConditionalProjectionMap<any, any>,
-  TKey extends string
+  TConfig extends ConditionalConfig
 > = SpreadableConditionals<
-  TKey,
-  | Empty
+  TConfig["key"],
+  | (TConfig["isExhaustive"] extends true ? never : Empty)
   | ValueOf<{
       [P in keyof TConditionalProjectionMap]: ExtractProjectionResult<
         TResultItem,
@@ -47,13 +47,12 @@ export type OmitConditionalProjections<TResultItem> = {
 };
 
 export type ExtractConditionalProjectionTypes<TProjectionMap> = Simplify<
-  | Empty
-  | IntersectionOfValues<{
-      [P in Extract<
-        keyof TProjectionMap,
-        ConditionalKey<string>
-      >]: InferResultType<Extract<TProjectionMap[P], IGroqBuilder>>;
-    }>
+  IntersectionOfValues<{
+    [P in Extract<
+      keyof TProjectionMap,
+      ConditionalKey<string>
+    >]: InferResultType<Extract<TProjectionMap[P], IGroqBuilder>>;
+  }>
 >;
 
 export type ConditionalByTypeProjectionMap<
@@ -72,10 +71,10 @@ export type ExtractConditionalByTypeProjectionResults<
     any,
     any
   >,
-  TKey extends string
+  TConfig extends ConditionalConfig
 > = SpreadableConditionals<
-  TKey,
-  | Empty
+  TConfig["key"],
+  | (TConfig["isExhaustive"] extends true ? never : Empty)
   | ValueOf<{
       [_type in keyof TConditionalByTypeProjectionMap]: ExtractProjectionResult<
         Extract<TResultItem, { _type: _type }>,
@@ -99,4 +98,10 @@ export type SpreadableConditionals<
   [UniqueConditionalKey in ConditionalKey<TKey>]: IGroqBuilder<ConditionalResultType>;
 };
 
-export type ConditionalConfig<TKey> = { key: TKey };
+export type ConditionalConfig<
+  TKey extends string = string,
+  TIsExhaustive extends boolean = boolean
+> = {
+  key: TKey;
+  isExhaustive: TIsExhaustive;
+};
diff --git a/packages/groq-builder/src/commands/conditionalByType.test.ts b/packages/groq-builder/src/commands/conditionalByType.test.ts
index 360c800..1ada883 100644
--- a/packages/groq-builder/src/commands/conditionalByType.test.ts
+++ b/packages/groq-builder/src/commands/conditionalByType.test.ts
@@ -103,6 +103,24 @@ describe("conditionalByType", () => {
     });
   });
 
+  it("types are correct when the conditions are exhaustive", () => {
+    const conditionsExhaustive = q.star
+      .filterByType("product", "variant")
+      .conditionalByType({
+        product: { _type: true, name: true },
+        variant: { _type: true, price: true },
+      });
+
+    type ActualItem = ExtractConditionalProjectionTypes<
+      typeof conditionsExhaustive
+    >;
+    type ExpectedItem =
+      | { _type: "product"; name: string }
+      | { _type: "variant"; price: number };
+
+    expectType<Simplify<ActualItem>>().toStrictEqual<ExpectedItem>();
+  });
+
   it("should be able to extract the return types", () => {
     type ConditionalResults = ExtractConditionalProjectionTypes<
       typeof conditionalByType
diff --git a/packages/groq-builder/src/commands/conditionalByType.ts b/packages/groq-builder/src/commands/conditionalByType.ts
index e743ae8..1266418 100644
--- a/packages/groq-builder/src/commands/conditionalByType.ts
+++ b/packages/groq-builder/src/commands/conditionalByType.ts
@@ -5,10 +5,10 @@ import {
   ExtractConditionalByTypeProjectionResults,
   ConditionalByTypeProjectionMap,
   ConditionalKey,
-  SpreadableConditionals,
   ConditionalConfig,
 } from "./conditional-types";
 import { ProjectionMap } from "./projection-types";
+import { IsEqual } from "../tests/expectType";
 
 declare module "../groq-builder" {
   export interface GroqBuilder<TResult, TRootConfig> {
@@ -17,14 +17,19 @@ declare module "../groq-builder" {
         ResultItem<TResult>,
         TRootConfig
       >,
-      TKey extends string = "[ByType]"
+      TKey extends string = "[ByType]",
+      TIsExhaustive extends boolean = TConditionalProjections extends Required<
+        ConditionalByTypeProjectionMap<ResultItem<TResult>, TRootConfig>
+      >
+        ? true
+        : false
     >(
       conditionalProjections: TConditionalProjections,
-      config?: ConditionalConfig<TKey>
+      config?: Partial<ConditionalConfig<TKey, TIsExhaustive>>
     ): ExtractConditionalByTypeProjectionResults<
       ResultItem<TResult>,
       TConditionalProjections,
-      TKey
+      ConditionalConfig<TKey, TIsExhaustive>
     >;
   }
 }
@@ -32,11 +37,12 @@ declare module "../groq-builder" {
 GroqBuilder.implement({
   conditionalByType<
     TConditionalProjections extends object,
-    TKey extends string
+    TKey extends string,
+    TIsExhaustive extends boolean
   >(
     this: GroqBuilder<any, RootConfig>,
     conditionalProjections: TConditionalProjections,
-    config?: ConditionalConfig<TKey>
+    config?: Partial<ConditionalConfig<TKey, TIsExhaustive>>
   ) {
     const typeNames = Object.keys(conditionalProjections);
 
@@ -63,15 +69,20 @@ GroqBuilder.implement({
           if (typeParser?.parser) {
             return typeParser.parser(input);
           }
+          if (!typeParser && config?.isExhaustive) {
+            throw new TypeError(
+              `Unexpected _type "${input._type}"; expected one of: ${typeNames}`
+            );
+          }
           return {};
         };
 
     const conditionalQuery = this.root.chain(query, conditionalParser);
-    const uniqueKey: ConditionalKey<string> = `[Conditional] ${
-      config?.key ?? ("[ByType]" as TKey)
-    }`;
+    const key: TKey = config?.key || ("[ByType]" as TKey);
+    const conditionalKey: ConditionalKey<TKey> = `[Conditional] ${key}`;
     return {
-      [uniqueKey]: conditionalQuery,
-    } as unknown as SpreadableConditionals<TKey, any>;
+      _type: true, // Ensure we request the `_type` parameter
+      [conditionalKey]: conditionalQuery,
+    } as any;
   },
 });