diff --git a/CONTRIBUTORS b/CONTRIBUTORS
index 9a07ecce..07cb746a 100644
--- a/CONTRIBUTORS
+++ b/CONTRIBUTORS
@@ -2627,6 +2627,7 @@ J
  for making cEpgHandlers::BeginSegmentTransfer() boolean
  for suggesting to change tEventID back to u_int32_t
  for adding the 'aux' member to cEvent
+ for reporting a possible deadlock when quickly zapping through encrypted channels
 
 Peter Pinnau <vdr@unterbrecher.de>
  for reporting that 'uint32_t' requires including stdint.h in font.h on some systems
diff --git a/HISTORY b/HISTORY
index 16d77b9b..0b412acb 100644
--- a/HISTORY
+++ b/HISTORY
@@ -9162,7 +9162,7 @@ Video Disk Recorder Revision History
   a subdirectory.
 - SVDRP peering can now be limited to the default SVDRP host (see MANUAL for details).
 
-2018-01-17: Version 2.3.9
+2018-01-28: Version 2.3.9
 
 - Updated the Italian OSD texts (thanks to Diego Pierotto).
 - Updated the Finnish OSD texts (thanks to Rolf Ahrenberg).
@@ -9245,3 +9245,5 @@ Video Disk Recorder Revision History
 - Now using the 'example' macro in vdr.5 (thanks to Chris Mayo).
 - Now unlocking the Recordings list before displaying an error message in
   cMenuPathEdit::ApplyChanges() and cReplayControl::Stop() (reported by Matthias Senzel).
+- Fixed a possible deadlock when quickly zapping through encrypted channels (reported
+  by Jörg Wendel).
diff --git a/ci.c b/ci.c
index b6ea3269..3eb40cb6 100644
--- a/ci.c
+++ b/ci.c
@@ -4,7 +4,7 @@
  * See the main source file 'vdr.c' for copyright information and
  * how to reach the author.
  *
- * $Id: ci.c 4.18 2017/06/19 12:13:38 kls Exp $
+ * $Id: ci.c 4.19 2018/01/28 11:14:40 kls Exp $
  */
 
 #include "ci.h"
@@ -122,6 +122,8 @@ private:
   uchar *bufp;
   uchar mtdCatBuffer[TS_SIZE]; // TODO: handle multi packet CATs!
   int length;
+  cMutex mutex;
+  bool handlingPid;
   void AddEmmPid(int Pid);
   void DelEmmPids(void);
 public:
@@ -130,6 +132,15 @@ public:
   virtual void Receive(const uchar *Data, int Length);
   bool HasCaPids(void) const { return NumPids() - emmPids.Size() - 1 > 0; }
   void Reset(void) { DelEmmPids(); catVersion = -1; }
+  bool HandlingPid(void);
+       ///< The cCaPidReceiver adds/deletes PIDs to/from the base class cReceiver,
+       ///< which in turn does the same on the cDevice it is attached to. The cDevice
+       ///< then sets the PIDs on the assigned cCamSlot, which can cause a deadlock on the
+       ///< cCamSlot's mutex if a cReceiver is detached from the device at the same time.
+       ///< Since these PIDs, however, are none that have to be decrypted,
+       ///< it is not necessary to set them in the CAM. Therefore this function is
+       ///< used in cCamSlot::SetPid() to detect this situation, and thus avoid the
+       ///< deadlock.
   };
 
 cCaPidReceiver::cCaPidReceiver(void)
@@ -137,7 +148,11 @@ cCaPidReceiver::cCaPidReceiver(void)
   catVersion = -1;
   bufp = NULL;
   length = 0;
+  handlingPid = false;
+  cMutexLock MutexLock(&mutex);
+  handlingPid = true;
   AddPid(CATPID);
+  handlingPid = false;
 }
 
 void cCaPidReceiver::AddEmmPid(int Pid)
@@ -147,14 +162,20 @@ void cCaPidReceiver::AddEmmPid(int Pid)
          return;
       }
   emmPids.Append(Pid);
+  cMutexLock MutexLock(&mutex);
+  handlingPid = true;
   AddPid(Pid);
+  handlingPid = false;
 }
 
 void cCaPidReceiver::DelEmmPids(void)
 {
+  cMutexLock MutexLock(&mutex);
+  handlingPid = true;
   for (int i = 0; i < emmPids.Size(); i++)
       DelPid(emmPids[i]);
   emmPids.Clear();
+  handlingPid = false;
 }
 
 void cCaPidReceiver::Receive(const uchar *Data, int Length)
@@ -239,6 +260,12 @@ void cCaPidReceiver::Receive(const uchar *Data, int Length)
      }
 }
 
+bool cCaPidReceiver::HandlingPid(void)
+{
+  cMutexLock MutexLock(&mutex);
+  return handlingPid;
+}
+
 // --- cCaActivationReceiver -------------------------------------------------
 
 // A receiver that is used to make the device stay on a given channel and
@@ -2588,6 +2615,8 @@ void cCamSlot::AddPid(int ProgramNumber, int Pid, int StreamType)
 
 void cCamSlot::SetPid(int Pid, bool Active)
 {
+  if (caPidReceiver && caPidReceiver->HandlingPid())
+     return;
   cMutexLock MutexLock(&mutex);
   for (cCiCaProgramData *p = caProgramList.First(); p; p = caProgramList.Next(p)) {
       for (cCiCaPidData *q = p->pidList.First(); q; q = p->pidList.Next(q)) {