diff --git a/lib/hmac-md5.c b/lib/hmac-md5.c
index 33f2bc9..935fa6e 100644
--- a/lib/hmac-md5.c
+++ b/lib/hmac-md5.c
@@ -15,6 +15,9 @@
    along with this program; if not, see <https://www.gnu.org/licenses/>.  */
 
 #include <config.h>
+
+#include "hmac.h"
+
 #include "md5.h"
 
 #define GL_HMAC_NAME 5
diff --git a/lib/hmac-sha1.c b/lib/hmac-sha1.c
index 8cab525..6f28bdc 100644
--- a/lib/hmac-sha1.c
+++ b/lib/hmac-sha1.c
@@ -15,6 +15,9 @@
    along with this program; if not, see <https://www.gnu.org/licenses/>.  */
 
 #include <config.h>
+
+#include "hmac.h"
+
 #include "sha1.h"
 
 #define GL_HMAC_NAME 1
diff --git a/lib/hmac-sha256.c b/lib/hmac-sha256.c
index f26a79f..16e4501 100644
--- a/lib/hmac-sha256.c
+++ b/lib/hmac-sha256.c
@@ -15,6 +15,9 @@
    along with this program; if not, see <https://www.gnu.org/licenses/>.  */
 
 #include <config.h>
+
+#include "hmac.h"
+
 #include "sha256.h"
 
 #define GL_HMAC_NAME 256
diff --git a/lib/hmac-sha512.c b/lib/hmac-sha512.c
index 91e5f98..6d919d0 100644
--- a/lib/hmac-sha512.c
+++ b/lib/hmac-sha512.c
@@ -15,6 +15,9 @@
    along with this program; if not, see <https://www.gnu.org/licenses/>.  */
 
 #include <config.h>
+
+#include "hmac.h"
+
 #include "sha512.h"
 
 #define GL_HMAC_NAME 512
diff --git a/lib/hmac.c b/lib/hmac.c
index fb9207f..00dd08f 100644
--- a/lib/hmac.c
+++ b/lib/hmac.c
@@ -16,7 +16,6 @@
 
 #include <string.h>
 
-#include "hmac.h"
 #include "memxor.h"
 
 #define IPAD 0x36
@@ -39,19 +38,34 @@
 #define GL_HMAC_FN_PROC _GLHMAC_CONCAT (HMAC_ALG, _process_bytes)
 #define GL_HMAC_FN_FINI _GLHMAC_CONCAT (HMAC_ALG, _finish_ctx)
 
+static void
+hmac_hash (const void *key, size_t keylen,
+           const void *in, size_t inlen,
+           int pad, void *resbuf)
+{
+  struct GL_HMAC_CTX hmac_ctx;
+  char block[GL_HMAC_BLOCKSIZE];
+
+  memset (block, pad, sizeof block);
+  /* zero padding of the key to the block size
+     is implicit in the memxor.  */
+  memxor (block, key, keylen);
+
+  GL_HMAC_FN_INIT (&hmac_ctx);
+  GL_HMAC_FN_BLOC (block, sizeof block, &hmac_ctx);
+  GL_HMAC_FN_PROC (in, inlen, &hmac_ctx);
+  GL_HMAC_FN_FINI (&hmac_ctx, resbuf);
+}
+
 int
 GL_HMAC_FN (const void *key, size_t keylen,
-             const void *in, size_t inlen, void *resbuf)
+            const void *in, size_t inlen, void *resbuf)
 {
-  struct GL_HMAC_CTX inner;
-  struct GL_HMAC_CTX outer;
   char optkeybuf[GL_HMAC_HASHSIZE];
-  char block[GL_HMAC_BLOCKSIZE];
   char innerhash[GL_HMAC_HASHSIZE];
 
   /* Ensure key size is <= block size.  */
-
-  if (keylen > sizeof block)
+  if (keylen > GL_HMAC_BLOCKSIZE)
     {
       struct GL_HMAC_CTX keyhash;
 
@@ -60,31 +74,14 @@ GL_HMAC_FN (const void *key, size_t keylen,
       GL_HMAC_FN_FINI (&keyhash, optkeybuf);
 
       key = optkeybuf;
-
-      /* zero padding of the key to the block size
-         is implicit in the memxor below.  */
       keylen = sizeof optkeybuf;
     }
 
   /* Compute INNERHASH from KEY and IN.  */
-
-  memset (block, IPAD, sizeof block);
-  memxor (block, key, keylen);
-
-  GL_HMAC_FN_INIT (&inner);
-  GL_HMAC_FN_BLOC (block, sizeof block, &inner);
-  GL_HMAC_FN_PROC (in, inlen, &inner);
-  GL_HMAC_FN_FINI (&inner, innerhash);
+  hmac_hash (key, keylen, in, inlen, IPAD, innerhash);
 
   /* Compute result from KEY and INNERHASH.  */
-
-  memset (block, OPAD, sizeof block);
-  memxor (block, key, keylen);
-
-  GL_HMAC_FN_INIT (&outer);
-  GL_HMAC_FN_BLOC (block, sizeof block, &outer);
-  GL_HMAC_FN_PROC (innerhash, sizeof innerhash, &outer);
-  GL_HMAC_FN_FINI (&outer, resbuf);
+  hmac_hash (key, keylen, innerhash, sizeof innerhash, OPAD, resbuf);
 
   return 0;
 }
diff --git a/tests/test-hmac-md5.c b/tests/test-hmac-md5.c
index 3110a84..199444b 100644
--- a/tests/test-hmac-md5.c
+++ b/tests/test-hmac-md5.c
@@ -17,11 +17,13 @@
 /* Written by Simon Josefsson.  */
 
 #include <config.h>
+
+#include "hmac.h"
+
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 
-#include "hmac.h"
 
 /* Test vectors from RFC 2104. */
 
diff --git a/tests/test-hmac-sha1.c b/tests/test-hmac-sha1.c
index 98a3b34..9d91876 100644
--- a/tests/test-hmac-sha1.c
+++ b/tests/test-hmac-sha1.c
@@ -17,12 +17,13 @@
 /* Written by Simon Josefsson.  */
 
 #include <config.h>
+
+#include "hmac.h"
+
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 
-#include "hmac.h"
-
 static void
 hmac_check (const void *key, size_t key_len,
             const void *data, size_t data_len, const char *digest)
diff --git a/tests/test-hmac-sha256.c b/tests/test-hmac-sha256.c
index 077ec6e..551e849 100644
--- a/tests/test-hmac-sha256.c
+++ b/tests/test-hmac-sha256.c
@@ -17,12 +17,13 @@
 /* Written by Simon Josefsson.  Test vectors from RFC 4231.  */
 
 #include <config.h>
+
+#include "hmac.h"
+
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 
-#include "hmac.h"
-
 static void
 hmac_check (const void *key, size_t key_len,
             const void *data, size_t data_len, const char *digest)
diff --git a/tests/test-hmac-sha512.c b/tests/test-hmac-sha512.c
index ab6e101..1ffe992 100644
--- a/tests/test-hmac-sha512.c
+++ b/tests/test-hmac-sha512.c
@@ -17,12 +17,13 @@
 /* Written by Simon Josefsson.  Test vectors from RFC 4231.  */
 
 #include <config.h>
+
+#include "hmac.h"
+
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 
-#include "hmac.h"
-
 static void
 hmac_check (const void *key, size_t key_len,
             const void *data, size_t data_len, const char *digest)