diff --git a/openssl/sha.go b/openssl/sha.go
index bb96a9b..12ef875 100644
--- a/openssl/sha.go
+++ b/openssl/sha.go
@@ -119,6 +119,26 @@ func (h *evpHash) Write(p []byte) (int, error) {
 	return len(p), nil
 }
 
+func (h *evpHash) WriteString(s string) (int, error) {
+	// TODO: use unsafe.StringData once we drop support
+	// for go1.19 and earlier.
+	hdr := (*struct {
+		Data *byte
+		Len  int
+	})(unsafe.Pointer(&s))
+	if len(s) > 0 && C.go_openssl_EVP_DigestUpdate(h.ctx, unsafe.Pointer(hdr.Data), C.size_t(len(s))) == 0 {
+		panic("openssl: EVP_DigestUpdate failed")
+	}
+	return len(s), nil
+}
+
+func (h *evpHash) WriteByte(c byte) error {
+	if C.go_openssl_EVP_DigestUpdate(h.ctx, unsafe.Pointer(&c), 1) == 0 {
+		panic("openssl: EVP_DigestUpdate failed")
+	}
+	return nil
+}
+
 func (h *evpHash) Size() int {
 	return h.size
 }
diff --git a/openssl/sha_test.go b/openssl/sha_test.go
index 7859b06..3169fcb 100644
--- a/openssl/sha_test.go
+++ b/openssl/sha_test.go
@@ -10,6 +10,7 @@ import (
 	"bytes"
 	"encoding"
 	"hash"
+	"io"
 	"testing"
 )
 
@@ -62,6 +63,23 @@ func TestSha(t *testing.T) {
 			if !bytes.Equal(sum, initSum) {
 				t.Errorf("got:%x want:%x", sum, initSum)
 			}
+
+			bw := h.(io.ByteWriter)
+			for i := 0; i < len(msg); i++ {
+				bw.WriteByte(msg[i])
+			}
+			h.Reset()
+			sum = h.Sum(nil)
+			if !bytes.Equal(sum, initSum) {
+				t.Errorf("got:%x want:%x", sum, initSum)
+			}
+
+			h.(io.StringWriter).WriteString(string(msg))
+			h.Reset()
+			sum = h.Sum(nil)
+			if !bytes.Equal(sum, initSum) {
+				t.Errorf("got:%x want:%x", sum, initSum)
+			}
 		})
 	}
 }