diff --git a/libavr b/libavr
index dc1e87d..43fc479 160000
--- a/libavr
+++ b/libavr
@@ -1 +1 @@
-Subproject commit dc1e87d86e8718c8d6d3b926dadfd5633995fdbf
+Subproject commit 43fc4796c2670e522233bd95a982a688052b9cf3
diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt
index 7274c3f..e5cb7e0 100644
--- a/test/CMakeLists.txt
+++ b/test/CMakeLists.txt
@@ -8,6 +8,10 @@ elseif(LIBAVR_MCU STREQUAL "attiny85")
 	libavr_size_claim_test(clock 1238)
 endif()
 
+# The README says the two modes emit the same image, and only a tree with
+# both built can say whether they do.
+libavr_mode_identity_test(clock)
+
 # The battery is a compile: a static_assert that fails is the failure. It is a
 # target rather than only a ctest so a plain build catches a regression too.
 add_library(consteval_tests OBJECT consteval.cpp)