diff --git a/httpie/cli/argparser.py b/httpie/cli/argparser.py
index cf096d8d..4a817b81 100644
--- a/httpie/cli/argparser.py
+++ b/httpie/cli/argparser.py
@@ -243,7 +243,7 @@ class HTTPieArgumentParser(argparse.ArgumentParser):
         Bytes are always read.
 
         """
-        if self.args.data:
+        if self.args.data or self.args.files:
             self.error('Request body (from stdin or a file) and request '
                        'data (key=value) cannot be mixed. Pass '
                        '--ignore-stdin to let key/value take priority. '