Index: packages/Python/lldbsuite/test/lldbtest.py
===================================================================
--- packages/Python/lldbsuite/test/lldbtest.py
+++ packages/Python/lldbsuite/test/lldbtest.py
@@ -2227,6 +2227,10 @@
         # Get the error text if there was an error, and the regular text if not.
         output = self.res.GetOutput() if self.res.Succeeded() \
                 else self.res.GetError()
+        # In Python 2, communicate sends byte strings. In Python 3, communicate sends bytes.
+        # If we got a string (and not a byte string), encode it before sending.
+        if isinstance(output, str) and not isinstance(output, bytes):
+            output = output.encode()
 
         # Assemble the absolute path to the check file. As a convenience for
         # LLDB inline tests, assume that the check file is a relative path to