diff --git a/src/host/dmr/Slot.cpp b/src/host/dmr/Slot.cpp
index 15c22cd7..4ff67e50 100644
--- a/src/host/dmr/Slot.cpp
+++ b/src/host/dmr/Slot.cpp
@@ -312,6 +312,8 @@ bool Slot::processFrame(uint8_t *data, uint32_t len)
 
 uint32_t Slot::peekFrameLength()
 {
+    std::lock_guard<std::mutex> lock(m_queueLock);
+
     if (m_txQueue.isEmpty() && m_txImmQueue.isEmpty())
         return 0U;
 
diff --git a/src/host/nxdn/Control.cpp b/src/host/nxdn/Control.cpp
index 746bfc82..13bab34a 100644
--- a/src/host/nxdn/Control.cpp
+++ b/src/host/nxdn/Control.cpp
@@ -465,6 +465,8 @@ bool Control::processFrame(uint8_t* data, uint32_t len)
 
 uint32_t Control::peekFrameLength()
 {
+    std::lock_guard<std::mutex> lock(m_queueLock);
+
     if (m_txQueue.isEmpty() && m_txImmQueue.isEmpty())
         return 0U;
 
diff --git a/src/host/p25/Control.cpp b/src/host/p25/Control.cpp
index 38befffa..e3449796 100644
--- a/src/host/p25/Control.cpp
+++ b/src/host/p25/Control.cpp
@@ -674,6 +674,8 @@ bool Control::processFrame(uint8_t* data, uint32_t len)
 
 uint32_t Control::peekFrameLength()
 {
+    std::lock_guard<std::mutex> lock(m_queueLock);
+
     if (m_txQueue.isEmpty() && m_txImmQueue.isEmpty())
         return 0U;