diff --git a/ext/digest/digest.c b/ext/digest/digest.c
index a02eb12..1731ebe 100644
--- a/ext/digest/digest.c
+++ b/ext/digest/digest.c
@@ -624,6 +624,7 @@ rb_digest_base_update(VALUE self, VALUE str)
     TypedData_Get_Struct(self, void, &digest_type, pctx);
 
     StringValue(str);
+    str = rb_str_new_frozen(str);
     algo->update_func(pctx, (unsigned char *)RSTRING_PTR(str), RSTRING_LEN(str));
     RB_GC_GUARD(str);
 
diff --git a/ext/digest/sha1/sha1.c b/ext/digest/sha1/sha1.c
index 5311227..547834f 100644
--- a/ext/digest/sha1/sha1.c
+++ b/ext/digest/sha1/sha1.c
@@ -18,6 +18,7 @@
  */
 
 #include "sha1.h"
+#include <ruby/thread.h>
 
 #define SHA1HANDSOFF		/* Copies data before messing with it. */
 
@@ -218,7 +219,7 @@ int SHA1_Init(SHA1_CTX *context)
 /*
  * Run your data through this.
  */
-void SHA1_Update(SHA1_CTX *context, const uint8_t *data, size_t len)
+static void SHA1_Update(SHA1_CTX *context, const uint8_t *data, size_t len)
 {
     uint32_t i, j;
 
@@ -241,11 +242,36 @@ void SHA1_Update(SHA1_CTX *context, const uint8_t *data, size_t len)
     (void)memcpy(&context->buffer[j], &data[i], len - i);
 }
 
+struct unpack_nogvl {
+    SHA1_CTX *context;
+    const uint8_t *data;
+    size_t len;
+};
+
+void * SHA1_UpdateNoGVLUnpack(void * ptr)
+{
+    struct unpack_nogvl * args;
+    args = ptr;
+    SHA1_Update(args->context, args->data, args->len);
+    return NULL;
+}
+
+void SHA1_UpdateNoGVL(SHA1_CTX *context, const uint8_t *data, size_t len)
+{
+    struct unpack_nogvl args;
+    args.context = context;
+    args.data = data;
+    args.len = len;
+
+    rb_thread_call_without_gvl(SHA1_UpdateNoGVLUnpack, &args, NULL, NULL);
+
+    return;
+}
 
 /*
  * Add padding and return the message digest.
  */
-int SHA1_Finish(SHA1_CTX* context, uint8_t digest[20])
+static int SHA1_Finish(SHA1_CTX* context, uint8_t digest[20])
 {
     size_t i;
     uint8_t finalcount[8];
@@ -269,3 +295,27 @@ int SHA1_Finish(SHA1_CTX* context, uint8_t digest[20])
     }
     return 1;
 }
+
+struct finish_nogvl {
+    SHA1_CTX *context;
+    uint8_t *digest;
+};
+
+void * SHA1_FinishNoGVLUnpack(void * ptr)
+{
+    struct finish_nogvl * args;
+    args = ptr;
+    SHA1_Finish(args->context, args->digest);
+    return NULL;
+}
+
+int SHA1_FinishNoGVL(SHA1_CTX* context, uint8_t digest[20])
+{
+    struct finish_nogvl args;
+    args.context = context;
+    args.digest = digest;
+
+    rb_thread_call_without_gvl(SHA1_FinishNoGVLUnpack, &args, NULL, NULL);
+    return 1;
+}
+
diff --git a/ext/digest/sha1/sha1.h b/ext/digest/sha1/sha1.h
index 6f1c388..4b24623 100644
--- a/ext/digest/sha1/sha1.h
+++ b/ext/digest/sha1/sha1.h
@@ -23,14 +23,12 @@ typedef struct {
 /* avoid name clash */
 #define SHA1_Transform	rb_Digest_SHA1_Transform
 #define SHA1_Init	rb_Digest_SHA1_Init
-#define SHA1_Update	rb_Digest_SHA1_Update
-#define SHA1_Finish	rb_Digest_SHA1_Finish
 #endif
 
 void	SHA1_Transform _((uint32_t state[5], const uint8_t buffer[64]));
 int	SHA1_Init _((SHA1_CTX *context));
-void	SHA1_Update _((SHA1_CTX *context, const uint8_t *data, size_t len));
-int	SHA1_Finish _((SHA1_CTX *context, uint8_t digest[20]));
+void	SHA1_UpdateNoGVL _((SHA1_CTX *context, const uint8_t *data, size_t len));
+int	SHA1_FinishNoGVL _((SHA1_CTX *context, uint8_t digest[20]));
 
 #define SHA1_BLOCK_LENGTH		64
 #define SHA1_DIGEST_LENGTH		20
diff --git a/ext/digest/sha1/sha1init.c b/ext/digest/sha1/sha1init.c
index 1f05808..cfef297 100644
--- a/ext/digest/sha1/sha1init.c
+++ b/ext/digest/sha1/sha1init.c
@@ -16,8 +16,8 @@ static const rb_digest_metadata_t sha1 = {
     SHA1_BLOCK_LENGTH,
     sizeof(SHA1_CTX),
     (rb_digest_hash_init_func_t)SHA1_Init,
-    (rb_digest_hash_update_func_t)SHA1_Update,
-    (rb_digest_hash_finish_func_t)SHA1_Finish,
+    (rb_digest_hash_update_func_t)SHA1_UpdateNoGVL,
+    (rb_digest_hash_finish_func_t)SHA1_FinishNoGVL,
 };
 
 /*