diff --git a/common/hsm_version.h b/common/hsm_version.h
index 3fd2135e0..41f179d69 100644
--- a/common/hsm_version.h
+++ b/common/hsm_version.h
@@ -4,6 +4,14 @@
 
 /* We give a maximum and minimum compatibility version to HSM, to allow
  * some API adaptation. */
+
+/* wire/hsmd_wire.csv contents version:
+ *    409cffa355ab6cc76bd298910adca9936a68223267ddc4815ba16aeac5d0acc3
+ */
 #define HSM_MIN_VERSION 1
+
+/* wire/hsmd_wire.csv contents version:
+ *    409cffa355ab6cc76bd298910adca9936a68223267ddc4815ba16aeac5d0acc3
+ */
 #define HSM_MAX_VERSION 1
 #endif /* LIGHTNING_COMMON_HSM_VERSION_H */
diff --git a/hsmd/Makefile b/hsmd/Makefile
index 6fd4dac59..40f74edb5 100644
--- a/hsmd/Makefile
+++ b/hsmd/Makefile
@@ -56,4 +56,10 @@ HSMD_COMMON_OBJS :=				\
 
 lightningd/lightning_hsmd: $(HSMD_OBJS) $(HSMD_COMMON_OBJS) $(BITCOIN_OBJS) $(WIRE_OBJS)
 
+check-source: check-hsm-versions
+
+# common/hsm_version.h should at least *mention* this!
+check-hsm-versions: hsmd/hsmd_wire.csv common/hsm_version.h
+	@SUM=`grep -vE '^(#| *$$)' hsmd/hsmd_wire.csv  | sha256sum | cut -c1-64`; if ! grep -q "$$SUM" common/hsm_version.h; then echo "*** hsmd_wire.csv changed to $$SUM without update to common/hsm_version.h">&2; exit 1; fi
+
 -include hsmd/test/Makefile