diff --git a/libs/ardour/ardour/plugin_insert.h b/libs/ardour/ardour/plugin_insert.h
index 0a56373972..5460e25a14 100644
--- a/libs/ardour/ardour/plugin_insert.h
+++ b/libs/ardour/ardour/plugin_insert.h
@@ -367,7 +367,24 @@ private:
 	/** details of the match currently being used */
 	Match _match;
 
-	typedef std::map <uint32_t, ARDOUR::ChanMapping> PinMappings;
+	/* ordered map [plugin instance ID] => ARDOUR::ChanMapping
+	 * TODO: consider replacing with boost::flat_map<> or std::vector<>.
+	 */
+	class PinMappings : public std::map <uint32_t, ARDOUR::ChanMapping> {
+		public:
+			/* this emulates C++11's  std::map::at()
+			 * return mapping for given plugin instance */
+			inline ARDOUR::ChanMapping const& p (const uint32_t i) const {
+#ifndef NDEBUG
+				const_iterator x = find (i);
+				assert (x != end ());
+				return x->second;
+#else
+				return find(i)->second;
+#endif
+			}
+	};
+
 	PinMappings _in_map;
 	PinMappings _out_map;
 	ChanMapping _thru_map; // out-idx <=  in-idx
diff --git a/libs/ardour/plugin_insert.cc b/libs/ardour/plugin_insert.cc
index b24d065b5b..f2ba464665 100644
--- a/libs/ardour/plugin_insert.cc
+++ b/libs/ardour/plugin_insert.cc
@@ -860,11 +860,11 @@ PluginInsert::connect_and_run (BufferSet& bufs, samplepos_t start, samplepos_t e
 				continue;
 			}
 			bool valid;
-			uint32_t first_idx = in_map.at(0).get (*t, 0, &valid);
+			uint32_t first_idx = in_map.p(0).get (*t, 0, &valid);
 			assert (valid && first_idx == 0); // check_inplace ensures this
 			/* copy the first stream's buffer contents to the others */
 			for (uint32_t i = 1; i < natural_input_streams ().get (*t); ++i) {
-				uint32_t idx = in_map.at(0).get (*t, i, &valid);
+				uint32_t idx = in_map.p(0).get (*t, i, &valid);
 				if (valid) {
 					assert (idx == 0);
 					bufs.get (*t, i).read_from (bufs.get (*t, first_idx), nframes, offset, offset);
@@ -950,7 +950,7 @@ PluginInsert::connect_and_run (BufferSet& bufs, samplepos_t start, samplepos_t e
 			for (DataType::iterator t = DataType::begin(); t != DataType::end(); ++t) {
 				for (uint32_t out = 0; out < natural_output_streams().get (*t); ++out) {
 					bool valid;
-					uint32_t out_idx = out_map.at(pc).get (*t, out, &valid);
+					uint32_t out_idx = out_map.p(pc).get (*t, out, &valid);
 					if (valid) {
 						used_outputs.set (*t, out_idx, 1); // mark as used
 					}
@@ -982,14 +982,14 @@ PluginInsert::connect_and_run (BufferSet& bufs, samplepos_t start, samplepos_t e
 		for (Plugins::iterator i = _plugins.begin(); i != _plugins.end(); ++i, ++pc) {
 
 			ARDOUR::ChanMapping i_in_map (natural_input_streams());
-			ARDOUR::ChanMapping i_out_map (out_map.at(pc));
+			ARDOUR::ChanMapping i_out_map (out_map.p(pc));
 			ARDOUR::ChanCount mapped;
 
 			/* map inputs sequentially */
 			for (DataType::iterator t = DataType::begin(); t != DataType::end(); ++t) {
 				for (uint32_t in = 0; in < natural_input_streams().get (*t); ++in) {
 					bool valid;
-					uint32_t in_idx = in_map.at(pc).get (*t, in, &valid);
+					uint32_t in_idx = in_map.p(pc).get (*t, in, &valid);
 					uint32_t m = mapped.get (*t);
 					if (valid) {
 						inplace_bufs.get (*t, m).read_from (bufs.get (*t, in_idx), nframes, offset, offset);
@@ -1035,7 +1035,7 @@ PluginInsert::connect_and_run (BufferSet& bufs, samplepos_t start, samplepos_t e
 		/* in-place processing */
 		uint32_t pc = 0;
 		for (Plugins::iterator i = _plugins.begin(); i != _plugins.end(); ++i, ++pc) {
-			if ((*i)->connect_and_run(bufs, start, end, speed, in_map.at(pc), out_map.at(pc), nframes, offset)) {
+			if ((*i)->connect_and_run(bufs, start, end, speed, in_map.p(pc), out_map.p(pc), nframes, offset)) {
 				deactivate ();
 			}
 		}