@@ -1,7 +1,7 @@
 /*
- * Copyright (c) 2008-2021 Jonathan Schleifer <js@nil.im>
+ * Copyright (c) 2008-2022 Jonathan Schleifer <js@nil.im>
  *
  * All rights reserved.
  *
  * This file is part of ObjFW. It may be distributed under the terms of the
  * Q Public License 1.0, which can be found in the file LICENSE.QPL included in
@@ -20,10 +20,11 @@
 
 #import "OFSHA224Or256Hash.h"
 #import "OFSecureData.h"
 
 #import "OFHashAlreadyCalculatedException.h"
+#import "OFHashNotCalculatedException.h"
 #import "OFOutOfRangeException.h"
 
 static const size_t blockSize = 64;
 
 @interface OFSHA224Or256Hash ()
@@ -232,12 +233,21 @@
 	}
 }
 
 - (const unsigned char *)digest
 {
+	if (!_calculated)
+		@throw [OFHashNotCalculatedException exceptionWithObject: self];
+
+	return (const unsigned char *)_iVars->state;
+}
+
+- (void)calculate
+{
 	if (_calculated)
-		return (const unsigned char *)_iVars->state;
+		@throw [OFHashAlreadyCalculatedException
+		    exceptionWithObject: self];
 
 	_iVars->buffer.bytes[_iVars->bufferLength] = 0x80;
 	OFZeroMemory(_iVars->buffer.bytes + _iVars->bufferLength + 1,
 	    64 - _iVars->bufferLength - 1);
 
@@ -253,12 +263,10 @@
 
 	processBlock(_iVars->state, _iVars->buffer.words);
 	OFZeroMemory(&_iVars->buffer, sizeof(_iVars->buffer));
 	byteSwapVectorIfLE(_iVars->state, 8);
 	_calculated = true;
-
-	return (const unsigned char *)_iVars->state;
 }
 
 - (void)reset
 {
 	[self of_resetState];