diff --git a/conf.d/ysigchan.conf.sample b/conf.d/ysigchan.conf.sample
index d29a4803..b9fbe5d8 100644
--- a/conf.d/ysigchan.conf.sample
+++ b/conf.d/ysigchan.conf.sample
@@ -402,6 +402,10 @@
 ; Defaults to yes
 ;confirm_ccr=yes
 
+; drop_unknown: boolean: Drop call or attempt to change circuit if an unknown
+;  or unsupported message is received in an early state
+;drop_unknown=yes
+
 ; ignore-grs-single: boolean: Ignore (drop) circuit group reset messages with
 ;  range 0 (1 circuit affected)
 ; Defaults to no
diff --git a/libs/ysig/isup.cpp b/libs/ysig/isup.cpp
index 4ea90b5a..fd137c9d 100644
--- a/libs/ysig/isup.cpp
+++ b/libs/ysig/isup.cpp
@@ -3055,6 +3055,7 @@ SS7ISUP::SS7ISUP(const NamedList& params, unsigned char sio)
       m_defaultSls(SlsLatest),
       m_maxCalledDigits(16),
       m_confirmCCR(true),
+      m_dropOnUnknown(true),
       m_ignoreGRSSingle(false),
       m_ignoreCGBSingle(false),
       m_ignoreCGUSingle(false),
@@ -3156,6 +3157,7 @@ SS7ISUP::SS7ISUP(const NamedList& params, unsigned char sio)
 
     m_continuity = params.getValue("continuity");
     m_confirmCCR = params.getBoolValue("confirm_ccr",true);
+    m_dropOnUnknown = params.getBoolValue("drop_unknown",true);
     m_ignoreGRSSingle = params.getBoolValue("ignore-grs-single");
     m_ignoreCGBSingle = params.getBoolValue("ignore-cgb-single");
     m_ignoreCGUSingle = params.getBoolValue("ignore-cgu-single");
@@ -3221,6 +3223,7 @@ bool SS7ISUP::initialize(const NamedList* config)
 	m_earlyAcm = config->getBoolValue("earlyacm",m_earlyAcm);
 	m_continuity = config->getValue("continuity",m_continuity);
 	m_confirmCCR = config->getBoolValue("confirm_ccr",true);
+	m_dropOnUnknown = config->getBoolValue("drop_unknown",true);
 	m_ignoreGRSSingle = config->getBoolValue("ignore-grs-single");
 	m_ignoreCGBSingle = config->getBoolValue("ignore-cgb-single");
 	m_ignoreCGUSingle = config->getBoolValue("ignore-cgu-single");
@@ -4874,7 +4877,7 @@ void SS7ISUP::processControllerMsg(SS7MsgISUP* msg, const SS7Label& label, int s
 	    if (call)
 		call->ref();
 	    unlock();
-	    if (call && call->earlyState()) {
+	    if (m_dropOnUnknown && call && call->earlyState()) {
 		Debug(this,DebugNote,
 		    "Received unexpected message for call %u (%p) in initial state",
 		    msg->cic(),call);
diff --git a/libs/ysig/yatesig.h b/libs/ysig/yatesig.h
index a712b2bd..83d1badb 100644
--- a/libs/ysig/yatesig.h
+++ b/libs/ysig/yatesig.h
@@ -8348,6 +8348,7 @@ private:
     String m_format;                     // Default format
     String m_continuity;                 // Continuity test type
     bool m_confirmCCR;                   // Send LPA in response to CCR
+    bool m_dropOnUnknown;                // Drop call in early state on unknown message
     bool m_ignoreGRSSingle;              // Ignore (drop) GRS with range 0 (1 circuit affected)
     bool m_ignoreCGBSingle;              // Ignore (drop) CGB with range 0 (1 circuit in map)
     bool m_ignoreCGUSingle;              // Ignore (drop) CGU with range 0 (1 circuit in map)