diff --git a/kmod/Makefile b/kmod/Makefile
index e8e45a4a..97c48c17 100644
--- a/kmod/Makefile
+++ b/kmod/Makefile
@@ -16,7 +16,11 @@ SCOUTFS_GIT_DESCRIBE := \
 	$(shell git describe --all --abbrev=6 --long 2>/dev/null || \
 		echo not-in-a-git-repository)
 
+SCOUTFS_FORMAT_HASH := \
+	$(shell cat src/format.h src/ioctl.h | md5sum | cut -b1-16)
+
 SCOUTFS_ARGS := SCOUTFS_GIT_DESCRIBE=$(SCOUTFS_GIT_DESCRIBE) \
+		SCOUTFS_FORMAT_HASH=$(SCOUTFS_FORMAT_HASH) \
 		CONFIG_SCOUTFS_FS=m -C $(SK_KSRC) M=$(CURDIR)/src \
 		EXTRA_CFLAGS=-Werror
 
diff --git a/kmod/src/Makefile b/kmod/src/Makefile
index 30997479..ed9bdcbe 100644
--- a/kmod/src/Makefile
+++ b/kmod/src/Makefile
@@ -1,6 +1,7 @@
 obj-$(CONFIG_SCOUTFS_FS) := scoutfs.o
 
-CFLAGS_super.o = -DSCOUTFS_GIT_DESCRIBE=\"$(SCOUTFS_GIT_DESCRIBE)\"
+CFLAGS_super.o = -DSCOUTFS_GIT_DESCRIBE=\"$(SCOUTFS_GIT_DESCRIBE)\" \
+		 -DSCOUTFS_FORMAT_HASH=0x$(SCOUTFS_FORMAT_HASH)LLU
 
 CFLAGS_scoutfs_trace.o = -I$(src) # define_trace.h double include
  
diff --git a/kmod/src/format.h b/kmod/src/format.h
index 9bc496b3..d9be949b 100644
--- a/kmod/src/format.h
+++ b/kmod/src/format.h
@@ -430,6 +430,7 @@ struct scoutfs_inet_addr {
 struct scoutfs_super_block {
 	struct scoutfs_block_header hdr;
 	__le64 id;
+	__le64 format_hash;
 	__u8 uuid[SCOUTFS_UUID_BYTES];
 	__le64 next_ino;
 	__le64 next_seq;
diff --git a/kmod/src/super.c b/kmod/src/super.c
index e3d81395..83dabb5e 100644
--- a/kmod/src/super.c
+++ b/kmod/src/super.c
@@ -184,6 +184,13 @@ int scoutfs_read_supers(struct super_block *sb,
 			continue;
 		}
 
+		if (super->format_hash != cpu_to_le64(SCOUTFS_FORMAT_HASH)) {
+			scoutfs_warn(sb, "super block %u has invalid format hash 0x%llx, expected 0x%llx",
+				     i, le64_to_cpu(super->format_hash),
+				     SCOUTFS_FORMAT_HASH);
+			continue;
+		}
+
 		if (found < 0 || (le64_to_cpu(super->hdr.seq) > seq)) {
 			*local = *super;
 			seq = le64_to_cpu((*local).hdr.seq);