diff --git a/src/build/make.ts b/src/build/make.ts
index f2860e9..3d61f04 100644
--- a/src/build/make.ts
+++ b/src/build/make.ts
@@ -236,6 +236,13 @@ PRODUCT_MANUFACTURER := ${mk.manufacturer}`)
     blocks.push(`PRODUCT_ENFORCE_RRO_TARGETS := ${mk.enforceRros}`)
   }
 
+  let extraMakefiles = config?.platform?.extra_product_makefiles
+  if (extraMakefiles !== undefined && extraMakefiles.length > 0) {
+    for (let mk of extraMakefiles) {
+      blocks.push(`include ${mk}`)
+    }
+  }
+
   let build_id = config?.device?.build_id
 
   if (build_id !== undefined) {
diff --git a/src/commands/generate-prep.ts b/src/commands/generate-prep.ts
index a70ab98..6b14415 100644
--- a/src/commands/generate-prep.ts
+++ b/src/commands/generate-prep.ts
@@ -127,6 +127,10 @@ export default class GeneratePrep extends Command {
           buildId = flags.buildId
         }
 
+        // these makefiles are expected to reference proprietary files that are
+        // inaccessible during state collection build
+        config.platform.extra_product_makefiles = []
+
         await doDevice(config, stockSrc, buildId, flags.skipCopy, flags.useTemp)
       },
       config => config.device.name,
diff --git a/src/config/device.ts b/src/config/device.ts
index b649331..9c1ae17 100644
--- a/src/config/device.ts
+++ b/src/config/device.ts
@@ -38,6 +38,8 @@ export interface DeviceConfig {
     namespaces: string[]
     sepolicy_dirs: string[]
     product_makefile: string // required
+    // not included in makefile for state collection build (generate-prep)
+    extra_product_makefiles: string[]
   }
 
   generate: {
@@ -99,6 +101,7 @@ const DEFAULT_CONFIG_BASE = {
   platform: {
     namespaces: [],
     sepolicy_dirs: [],
+    extra_product_makefiles: [],
   },
   generate: {
     overrides: true,