Index: src/OFExceptions.h
==================================================================
--- src/OFExceptions.h
+++ src/OFExceptions.h
@@ -685,5 +685,17 @@
 /**
  * An OFException indicating that the thread has been canceled.
  */
 @interface OFThreadCanceledException: OFException {}
 @end
+
+/**
+ * An OFException indicating that locking a mutex failed.
+ */
+@interface OFMutexLockFailedException: OFException {}
+@end
+
+/**
+ * An OFException indicating that unlocking a mutex failed.
+ */
+@interface OFMutexUnlockFailedException: OFException {}
+@end

Index: src/OFExceptions.m
==================================================================
--- src/OFExceptions.m
+++ src/OFExceptions.m
@@ -994,8 +994,34 @@
 
 	string = [[OFString alloc] initWithFormat:
 	    @"The requested action cannot be performed because the thread of "
 	    @"class %s was canceled!", [class_ className]];
 
+	return string;
+}
+@end
+
+@implementation OFMutexLockFailedException
+- (OFString*)string
+{
+	if (string != nil)
+		return string;
+
+	string = [[OFString alloc] initWithFormat:
+	    @"A mutex could not be locked in class %s", [class_ className]];
+
+	return string;
+}
+@end
+
+@implementation OFMutexUnlockFailedException
+- (OFString*)string
+{
+	if (string != nil)
+		return string;
+
+	string = [[OFString alloc] initWithFormat:
+	    @"A mutex could not be unlocked in class %s", [class_ className]];
+
 	return string;
 }
 @end

Index: src/OFThread.m
==================================================================
--- src/OFThread.m
+++ src/OFThread.m
@@ -165,27 +165,26 @@
 	return self;
 }
 
 - lock
 {
-	/* FIXME: Add error-handling */
-	of_mutex_lock(&mutex);
+	if (!of_mutex_lock(&mutex))
+		@throw [OFMutexLockFailedException newWithClass: isa];
 
 	return self;
 }
 
 - unlock
 {
-	/* FIXME: Add error-handling */
-	of_mutex_unlock(&mutex);
+	if (!of_mutex_unlock(&mutex))
+		@throw [OFMutexUnlockFailedException newWithClass: isa];
 
 	return self;
 }
 
 - (void)dealloc
 {
-	/* FIXME: Add error-handling */
 	of_mutex_free(&mutex);
 
 	[super dealloc];
 }
 @end