diff --git a/adb/adb_io.cpp b/adb/adb_io.cpp
index 6cc274b..e6fefda 100644
--- a/adb/adb_io.cpp
+++ b/adb/adb_io.cpp
@@ -38,7 +38,8 @@
 
     // The cost of sending two strings outweighs the cost of formatting.
     // "adb sync" performance is affected by this.
-    return WriteFdFmt(fd, "%04x%.*s", length, length, s.c_str());
+    auto str = android::base::StringPrintf("%04x", length).append(s);
+    return WriteFdExactly(fd, str);
 }
 
 bool ReadProtocolString(int fd, std::string* s, std::string* error) {
diff --git a/fastboot/device/flashing.cpp b/fastboot/device/flashing.cpp
index 963916c..f737405 100644
--- a/fastboot/device/flashing.cpp
+++ b/fastboot/device/flashing.cpp
@@ -143,6 +143,11 @@
         return device->WriteFail("Data is not a valid logical partition metadata image");
     }
 
+    if (!FindPhysicalPartition(super_name)) {
+        return device->WriteFail("Cannot find " + super_name +
+                                 ", build may be missing broken or missing boot_devices");
+    }
+
     // If we are unable to read the existing metadata, then the super partition
     // is corrupt. In this case we reflash the whole thing using the provided
     // image.