diff --git a/pw_build/BUILD.gn b/pw_build/BUILD.gn
index d02cde1..dfaad82 100644
--- a/pw_build/BUILD.gn
+++ b/pw_build/BUILD.gn
@@ -70,6 +70,7 @@
   cflags = [
     "-Wall",
     "-Wextra",
+    "-Wimplicit-fallthrough",
 
     # Make all warnings errors, except for the exemptions below.
     "-Werror",