diff --git a/libs/ardour/audio_unit.cc b/libs/ardour/audio_unit.cc
index af09bd82d6..697c5feb4c 100644
--- a/libs/ardour/audio_unit.cc
+++ b/libs/ardour/audio_unit.cc
@@ -1429,7 +1429,7 @@ AUPlugin::can_support_io_configuration (const ChanCount& in, ChanCount& out, Cha
 			continue;
 		}
 
-		/* now allow potentially "output-imprecise" matches */
+		/* now allow potentially "imprecise" matches */
 		if (possible_in == 0) {
 			/* no inputs, generators & instruments */
 			if (possible_out == -1 || possible_out == -2) {
@@ -1471,56 +1471,39 @@ AUPlugin::can_support_io_configuration (const ChanCount& in, ChanCount& out, Cha
 
 		if (possible_in < -2 || possible_in > 0) {
 			/* specified number, exact or up to */
-			if (possible_in < -2 && audio_in > -possible_in && !imprecise) {
-				/* request is too large */
-			} else if (possible_in > 0 && audio_in != possible_in) {
-				/* this configuration needed exacty possible_in inputs */
+			int32_t desired_in;
+			if (possible_in > 0) {
+				/* configuration can only match possible_in */
+				desired_in = possible_in;
+			} else {
+				/* configuration can match up to -possible_in */
+				desired_in = min (-possible_in, audio_in);
+			}
+			if (!imprecise && audio_in != desired_in) {
+				/* skip that configuration, it cannot match
+				 * the required audio input count, and we
+				 * cannot ask for change via \imprecise */
 			} else if (possible_out == -1 || possible_out == -2) {
 				/* any output configuration possible
-				 * out == -2 is invalid, interpreted as out == -1 */
-				FOUNDCFG (preferred_out);
+				 * out == -2 is invalid, interpreted as out == -1
+				 * Really imprecise only if desired_in != audio_in */
+				FOUNDCFG_IMPRECISE (desired_in, preferred_out);
 				ANYTHINGGOES;
 			} else if (possible_out < -2) {
 				/* variable number of outputs up to -N
-				 * not specified if in > 0, but we accept it anyway */
-				FOUNDCFG (min (-possible_out, preferred_out));
+				 * not specified if in > 0, but we accept it anyway
+				 * Really imprecise only if desired_in != audio_in */
+				FOUNDCFG_IMPRECISE (desired_in, min (-possible_out, preferred_out));
 				UPTO (-possible_out)
 			} else {
-				/* exact number of outputs */
-				FOUNDCFG (possible_out);
-			}
-			if (possible_in < -2 && audio_in > -possible_in && imprecise) {
-				// hide inputs ports
-				// XXX: this is really *input* imprecise and should have
-				// been part of the second pass below. Also, this change
-				// should only be applied when really selecting a corresponding
-				// configuration.
-				imprecise->set (DataType::AUDIO, -possible_in);
-			}
-		}
-
-	}
-
-	if (!found && imprecise) {
-		/* try harder */
-		for (vector<pair<int,int> >::iterator i = io_configs.begin(); i != io_configs.end(); ++i) {
-			int32_t possible_in = i->first;
-			int32_t possible_out = i->second;
-
-			assert (possible_in > 0); // all other cases will have been matched above
-
-			if (possible_out == -1 || possible_out == -2) {
-				FOUNDCFG_IMPRECISE (possible_in, 2);
-			} else if (possible_out < -2) {
-				/* explicitly variable number of outputs, pick maximum */
-				FOUNDCFG_IMPRECISE (possible_in, min (-possible_out, preferred_out));
-			} else {
-				/* exact number of outputs */
-				FOUNDCFG_IMPRECISE (possible_in, possible_out);
+				/* exact number of outputs
+				 * Really imprecise only if desired_in != audio_in */
+				FOUNDCFG_IMPRECISE (desired_in, possible_out);
 			}
 			// ideally we'll also find the closest, best matching
 			// input configuration with minimal output penalty...
 		}
+
 	}
 
 	if (!found) {