Index: src/OFHashes.m
==================================================================
--- src/OFHashes.m
+++ src/OFHashes.m
@@ -13,10 +13,11 @@
 
 #include <string.h>
 
 #import "OFHashes.h"
 #import "OFAutoreleasePool.h"
+#import "OFExceptions.h"
 #import "OFMacros.h"
 
 int _OFHashing_reference;
 
 /*******
@@ -138,15 +139,17 @@
 - updateWithBuffer: (const char*)buffer
 	    ofSize: (size_t)size
 {
 	uint32_t t;
 
-	if (calculated)
-		return self;
 	if (size == 0)
 		return self;
 
+	if (calculated)
+		/* FIXME: Maybe a new exception would be better */
+		@throw [OFInvalidArgumentException newWithClass: isa];
+
 	/* Update bitcount */
 	t = bits[0];
 	if ((bits[0] = t + ((uint32_t)size << 3)) < t)
 		/* Carry from low to high */
 		bits[1]++;
@@ -375,15 +378,17 @@
 }
 
 - updateWithBuffer: (const char*)buf
 	    ofSize: (size_t)size
 {
-	if (calculated)
-		return self;
 	if (size == 0)
 		return self;
 
+	if (calculated)
+		/* FIXME: Maybe a new exception would be better */
+		@throw [OFInvalidArgumentException newWithClass: isa];
+
 	sha1_update(state, &count, buffer, buf, size);
 
 	return self;
 }