Fixes
diff --git a/config.m4 b/config.m4
index c583ec4..5d92a2a 100644
--- a/config.m4
+++ b/config.m4
@@ -85,7 +85,7 @@
     src/core/lib/support/tmpfile_windows.cc \
     src/core/lib/support/wrap_memcpy.cc \
     src/core/lib/surface/init.cc \
-    src/core/lib/backoff/backoff.c \
+    src/core/lib/backoff/backoff.cc \
     src/core/lib/channel/channel_args.cc \
     src/core/lib/channel/channel_stack.cc \
     src/core/lib/channel/channel_stack_builder.cc \