diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,9 @@
 # Revision history for sha1
 
+## 0.1.0.1 -- 2020-03-09
+
+* Add `sha1.h` to `extra-source-files`.
+
 ## 0.1.0.0 -- 2020-03-09
 
 * Initial release
diff --git a/cbits/sha1.h b/cbits/sha1.h
new file mode 100644
--- /dev/null
+++ b/cbits/sha1.h
@@ -0,0 +1,55 @@
+/*
+ * Copyright (C) 2006-2009 Vincent Hanquez <vincent@snarc.org>
+ *               2016      Herbert Valerio Riedel <hvr@gnu.org>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+ * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+ * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef CRYPTOHASH_SHA1_H
+#define CRYPTOHASH_SHA1_H
+
+#include <stdint.h>
+#include <stddef.h>
+
+#include "Rts.h"
+
+struct sha1_ctx
+{
+  uint64_t sz;
+  uint8_t  buf[64];
+  uint32_t h[5];
+};
+
+#define SHA1_DIGEST_SIZE	20
+#define SHA1_CTX_SIZE 		92 /* NB: no 64-bit padding */
+
+void hs_cryptohash_sha1_init(struct sha1_ctx *ctx);
+void hs_cryptohash_sha1_update(struct sha1_ctx *ctx, const uint8_t *data, size_t len);
+void hs_cryptohash_sha1_finalize(struct sha1_ctx *ctx, uint8_t * restrict out);
+void hs_cryptohash_sha1_onepass
+  ( uint8_t * restrict out
+  , HsInt out_off
+  , const uint8_t *data
+  , HsInt data_off
+  , HsInt data_len
+  );
+
+#endif
diff --git a/sha1.cabal b/sha1.cabal
--- a/sha1.cabal
+++ b/sha1.cabal
@@ -1,6 +1,6 @@
 cabal-version: 2.2
 name: sha1
-version: 0.1.0.0
+version: 0.1.0.1
 synopsis: SHA-1 Hash
 description:
   This library is a copy of cryptohash-sha1 that works on GC-managed
@@ -16,7 +16,9 @@
 copyright: 2020 Andrew Martin
 category: Data
 build-type: Simple
-extra-source-files: CHANGELOG.md
+extra-source-files:
+  CHANGELOG.md
+  cbits/sha1.h
 
 library
   c-sources: cbits/sha1.c