Index: src/OFExceptions.h
==================================================================
--- src/OFExceptions.h
+++ src/OFExceptions.h
@@ -1170,10 +1170,16 @@
  * \brief An exception indicating that unlocking a mutex failed.
  */
 @interface OFMutexUnlockFailedException: OFException
 @end
 
+/**
+ * \brief An exception indicating that a mutex is still locked.
+ */
+@interface OFMutexLockedException: OFException
+@end
+
 /**
  * \brief An exception indicating that the hash has already been calculated.
  */
 @interface OFHashAlreadyCalculatedException: OFException
 @end

Index: src/OFExceptions.m
==================================================================
--- src/OFExceptions.m
+++ src/OFExceptions.m
@@ -1674,11 +1674,11 @@
 	if (description != nil)
 		return description;
 
 	description = [[OFString alloc] initWithFormat:
 	    @"Deallocation of a thread of type %@ was tried, even though it "
-	    @"was still running", inClass];
+	    @"was still running!", inClass];
 
 	return description;
 }
 @end
 
@@ -1687,11 +1687,11 @@
 {
 	if (description != nil)
 		return description;
 
 	description = [[OFString alloc] initWithFormat:
-	    @"A mutex could not be locked in class %@", inClass];
+	    @"A mutex of class %@ could not be locked!", inClass];
 
 	return description;
 }
 @end
 
@@ -1700,11 +1700,25 @@
 {
 	if (description != nil)
 		return description;
 
 	description = [[OFString alloc] initWithFormat:
-	    @"A mutex could not be unlocked in class %@", inClass];
+	    @"A mutex of class %@ could not be unlocked!", inClass];
+
+	return description;
+}
+@end
+
+@implementation OFMutexLockedException
+- (OFString*)description
+{
+	if (description != nil)
+		return description;
+
+	description = [[OFString alloc] initWithFormat:
+	    @"Deallocation of a mutex of type %@ was tried, even though it "
+	    @"was still locked!", inClass];
 
 	return description;
 }
 @end
 

Index: src/OFThread.m
==================================================================
--- src/OFThread.m
+++ src/OFThread.m
@@ -367,10 +367,11 @@
 }
 
 - (void)dealloc
 {
 	if (initialized)
-		of_mutex_free(&mutex);
+		if (!of_mutex_free(&mutex))
+			@throw [OFMutexLockedException newWithClass: isa];
 
 	[super dealloc];
 }
 @end