diff --git a/state.c b/state.c
index 7b98eb1a..b8e5cb22 100644
--- a/state.c
+++ b/state.c
@@ -745,9 +745,9 @@ void state_read(struct snapraid_state* state)
 		return;
 	}
 
-	/* start with a MD5 default. */
+	/* start with a undefined default. */
 	/* it's for compatibility with version 1.0 where MD5 was implicit. */
-	state->hash = HASH_MD5;
+	state->hash = HASH_UNDEFINED;
 
 	disk = 0;
 	file = 0;
@@ -1384,8 +1384,17 @@ void state_read(struct snapraid_state* state)
 
 	sclose(f);
 
+	if (state->hash == HASH_UNDEFINED) {
+		fprintf(stderr, "The checksum to use is not specified.\n");
+		fprintf(stderr, "This happens because you are likely upgrading from SnapRAID 1.0.\n");
+		fprintf(stderr, "To use the SnapRAID 2.x branch, you must restart from scratch,\n");
+		fprintf(stderr, "deleting all the content and parity files.\n");
+		exit(EXIT_FAILURE);
+	}
 	if (state->hash == HASH_MD5) {
-		fprintf(stderr, "MD5 is not supported anymore.\n");
+		fprintf(stderr, "The MD5 checksum is not supported anymore.\n");
+		fprintf(stderr, "To use the SnapRAID 2.x branch, you must restart from scratch,\n");
+		fprintf(stderr, "deleting all the content and parity files.\n");
 		exit(EXIT_FAILURE);
 	}
 
diff --git a/util.c b/util.c
index 3011f305..c33202c5 100644
--- a/util.c
+++ b/util.c
@@ -709,9 +709,14 @@ void* malloc_nofail_align(size_t size, void** freeptr)
 
 void memhash(unsigned kind, void* digest, const void* src, unsigned size)
 {
-	if (kind == HASH_MURMUR3) {
+	switch (kind) {
+	case HASH_MURMUR3 :
 		MurmurHash3_x86_128(src, size, 0, digest);
-		return;
+		break;
+	default:
+		fprintf(stderr, "Internal inconsistency in hash function %u\n", kind);
+		exit(EXIT_FAILURE);
+		break;
 	}
 }
 
diff --git a/util.h b/util.h
index 4572c379..f6bdf490 100644
--- a/util.h
+++ b/util.h
@@ -372,8 +372,9 @@ void* malloc_nofail_align(size_t size, void** freeptr);
 /**
  * Hash kinds.
  */
-#define HASH_MURMUR3 0
+#define HASH_UNDEFINED 0
 #define HASH_MD5 1
+#define HASH_MURMUR3 2
 
 /**
  * Computes the HASH of a memory block.