diff --git a/packages/cli/src/tools/config/index.js b/packages/cli/src/tools/config/index.js
index f265a2a41..0ba40ecec 100644
--- a/packages/cli/src/tools/config/index.js
+++ b/packages/cli/src/tools/config/index.js
@@ -124,7 +124,7 @@ function loadConfig(projectRoot: string = process.cwd()): ConfigT {
       get assets() {
         return findAssets(projectRoot, userConfig.assets);
       },
-      platforms: {},
+      platforms: userConfig.platforms,
       haste: {
         providesModuleNodeModules: [],
         platforms: [],
diff --git a/packages/cli/src/tools/config/schema.js b/packages/cli/src/tools/config/schema.js
index a46f03776..cd2870afe 100644
--- a/packages/cli/src/tools/config/schema.js
+++ b/packages/cli/src/tools/config/schema.js
@@ -85,12 +85,13 @@ export const dependencyConfig = t
         projectConfig: t.func(),
         linkConfig: t.func(),
       }),
-    ).default(),
+    ).default({}),
     commands: t
       .array()
       .items(command)
       .default([]),
   })
+  .unknown(true)
   .default();
 
 /**
@@ -170,5 +171,14 @@ export const projectConfig = t
       .array()
       .items(command)
       .default([]),
+    platforms: map(
+      t.string(),
+      t.object({
+        dependencyConfig: t.func(),
+        projectConfig: t.func(),
+        linkConfig: t.func(),
+      }),
+    ).default({}),
   })
+  .unknown(true)
   .default();
diff --git a/types/index.js b/types/index.js
index feef6bcd2..67178942f 100644
--- a/types/index.js
+++ b/types/index.js
@@ -195,10 +195,10 @@ export type UserDependencyConfigT = {
  */
 export type UserConfigT = {
   /**
-   * Shares some structure with ConfigT, except that haste, root, platforms
+   * Shares some structure with ConfigT, except that haste and root
    * are calculated and can't be defined
    */
-  ...$Diff<ConfigT, {haste: any, root: any, platforms: any}>,
+  ...$Diff<ConfigT, {haste: any, root: any}>,
   reactNativePath: ?string,
 
   // Additional project settings