diff --git a/conda_build/build.py b/conda_build/build.py
index 71b403cfb5..8b544ed11c 100644
--- a/conda_build/build.py
+++ b/conda_build/build.py
@@ -1847,14 +1847,16 @@ def bundle_conda(output, metadata: MetaData, env, stats, **kw):
         interpreter = output.get("script_interpreter")
         if not interpreter:
             interpreter_and_args = guess_interpreter(output["script"])
+            log.debug("guess_interpreter yielded: %s", interpreter_and_args)
             interpreter_and_args[0] = external.find_executable(
                 interpreter_and_args[0], metadata.config.build_prefix
             )
+            log.debug("find_executable yielded: %s", interpreter_and_args[0])
             if not interpreter_and_args[0]:
                 log.error(
-                    "Did not find an interpreter to run {}, looked for {}".format(
-                        output["script"], interpreter_and_args[0]
-                    )
+                    "Did not find an interpreter to run %s, looked for %s",
+                    output["script"],
+                    interpreter_and_args[0],
                 )
             if (
                 "system32" in interpreter_and_args[0]