diff --git a/src/block/block.cpp b/src/block/block.cpp
index 96fcc3069..c8b15b7bb 100644
--- a/src/block/block.cpp
+++ b/src/block/block.cpp
@@ -132,10 +132,13 @@ void Block::update_diffpairs()
     }
     for (auto &it : nets) {
         if (it.second.diffpair_primary) {
-            if (nets.count(it.second.diffpair.uuid))
+            if (nets.count(it.second.diffpair.uuid)) {
                 it.second.diffpair->diffpair = &it.second;
-            else
+            }
+            else {
                 it.second.diffpair = nullptr;
+                it.second.diffpair_primary = false;
+            }
         }
     }
 }
diff --git a/src/block/net.cpp b/src/block/net.cpp
index 949d945b9..c2de1b22e 100644
--- a/src/block/net.cpp
+++ b/src/block/net.cpp
@@ -55,7 +55,7 @@ json Net::serialize() const
     j["net_class"] = net_class->uuid;
     j["power_symbol_name_visible"] = power_symbol_name_visible;
     j["power_symbol_style"] = power_symbol_style_lut.lookup_reverse(power_symbol_style);
-    if (diffpair_primary)
+    if (diffpair_primary && diffpair)
         j["diffpair"] = diffpair->uuid;
     j["is_port"] = is_port;
     j["port_direction"] = Pin::direction_lut.lookup_reverse(port_direction);
diff --git a/src/router/pns_horizon_iface.cpp b/src/router/pns_horizon_iface.cpp
index d49eb50d7..bd52e5aaa 100644
--- a/src/router/pns_horizon_iface.cpp
+++ b/src/router/pns_horizon_iface.cpp
@@ -304,7 +304,7 @@ bool PNS_HORIZON_RULE_RESOLVER::DpNetPair(const PNS::ITEM *aItem, int &aNetP, in
         return false;
     auto net = m_iface->get_net_for_code(aItem->Net());
     if (net->diffpair) {
-        if (net->diffpair_primary) {
+        if (net->diffpair_primary && net->diffpair) {
             aNetP = m_iface->get_net_code(net->uuid);
             aNetN = m_iface->get_net_code(net->diffpair->uuid);
         }