diff --git a/electrum/interface.py b/electrum/interface.py
index 82b707c57..850d5d9ea 100644
--- a/electrum/interface.py
+++ b/electrum/interface.py
@@ -598,6 +598,8 @@ class Interface(Logger):
         self.logger.info("cert fingerprint verification passed")
 
     async def get_block_header(self, height, assert_mode):
+        if not is_non_negative_integer(height):
+            raise Exception(f"{repr(height)} is not a block height")
         self.logger.info(f'requesting block header {height} in mode {assert_mode}')
         # use lower timeout as we usually have network.bhi_lock here
         timeout = self.network.get_network_timeout_seconds(NetworkTimeout.Urgent)