diff --git a/adb/adb.c b/adb/adb.c
index 95d3921..f3251fe 100644
--- a/adb/adb.c
+++ b/adb/adb.c
@@ -1024,7 +1024,13 @@
 
     // Our external storage path may be different than apps, since
     // we aren't able to bind mount after dropping root.
-    setenv("EXTERNAL_STORAGE", getenv("ADB_EXTERNAL_STORAGE"), 1);
+    const char* adb_external_storage = getenv("ADB_EXTERNAL_STORAGE");
+    if (NULL != adb_external_storage) {
+        setenv("EXTERNAL_STORAGE", adb_external_storage, 1);
+    } else {
+        D("Warning: ADB_EXTERNAL_STORAGE is not set.  Leaving EXTERNAL_STORAGE"
+          " unchanged.\n");
+    }
 
     /* don't listen on a port (default 5037) if running in secure mode */
     /* don't run as root if we are running in secure mode */