diff --git a/kernel/drivertools.cc b/kernel/drivertools.cc
index f0dda51a8b8..720125e1070 100644
--- a/kernel/drivertools.cc
+++ b/kernel/drivertools.cc
@@ -97,7 +97,10 @@ bool DriveChunkWire::try_append(DriveChunkWire const &chunk)
     return true;
 }
 
-bool DriveChunkPort::can_append(DriveBitPort const &bit) const { return bit.cell == cell && bit.port == port && bit.offset == offset + width; }
+bool DriveChunkPort::can_append(DriveBitPort const &bit) const
+{
+    return bit.cell == cell && bit.port == port && bit.offset == offset + width;
+}
 
 bool DriveChunkPort::try_append(DriveBitPort const &bit)
 {
@@ -683,15 +686,9 @@ void DriverMap::add(DriveBit const &a, DriveBit const &b)
         connect_directed_merge(b_id, a_id);
     // If either bit requires a driven value and has a unique driver, merge
     // and use the other end as representative bit.
-    else if (a_mode == BitMode::DRIVEN_UNIQUE)
-        connect_directed_merge(a_id, b_id);
-    else if (b_mode == BitMode::DRIVEN_UNIQUE)
-        connect_directed_merge(b_id, a_id);
-    // If either bit requires a driven value and may have multiple drivers,
-    // store a directed connection from the other bit.
-    else if (a_mode == BitMode::DRIVEN)
+    else if (a_mode == BitMode::DRIVEN_UNIQUE && !(b_mode == BitMode::DRIVEN_UNIQUE || b_mode == BitMode::DRIVEN))
         connect_directed_buffer(a_id, b_id);
-    else if (b_mode == BitMode::DRIVEN)
+    else if (b_mode == BitMode::DRIVEN_UNIQUE && !(b_mode == BitMode::DRIVEN_UNIQUE || b_mode == BitMode::DRIVEN))
         connect_directed_buffer(b_id, a_id);
     // If either bit only drives a value, store a directed connection from
     // it to the other bit.
@@ -933,15 +930,15 @@ const char *log_signal(DriveSpec const &spec)
 		return log_signal(chunks[0]);
 
 	std::string str;
-	const char *sep = "{";
+	const char *sep = "{ ";
 
 	for (auto i = chunks.rbegin(), end = chunks.rend(); i != end; ++i)
 	{
 		str += sep;
-		sep = ", ";
+		sep = " ";
 		str += log_signal(*i);
 	}
-	str += "}";
+	str += " }";
 
 	return log_str(str);
 }
diff --git a/kernel/drivertools.h b/kernel/drivertools.h
index cb562b016a1..b440afddaa2 100644
--- a/kernel/drivertools.h
+++ b/kernel/drivertools.h
@@ -445,7 +445,7 @@ struct DriveBit
 
 	DriveType type() const { return type_; }
 
-	bool is_undriven() const { return type_ == DriveType::NONE; }
+	bool is_none() const { return type_ == DriveType::NONE; }
 	bool is_constant() const { return type_ == DriveType::CONSTANT; }
 	bool is_wire() const { return type_ == DriveType::WIRE; }
 	bool is_port() const { return type_ == DriveType::PORT; }
@@ -723,6 +723,7 @@ struct DriveChunk
 		switch (type_)
 		{
 			case DriveType::NONE:
+				none_ = width;
 				break;
 			case DriveType::CONSTANT:
 				constant_.~Const();
@@ -749,7 +750,7 @@ struct DriveChunk
 		switch (other.type_)
 		{
 			case DriveType::NONE:
-				set_none();
+				set_none(other.none_);
 				break;
 			case DriveType::CONSTANT:
 				*this = other.constant_;
@@ -775,7 +776,7 @@ struct DriveChunk
 		switch (other.type_)
 		{
 			case DriveType::NONE:
-				set_none();
+				set_none(other.none_);
 				break;
 			case DriveType::CONSTANT:
 				*this = std::move(other.constant_);
@@ -989,7 +990,7 @@ struct DriveChunk
 
 	DriveType type() const { return type_; }
 
-	bool is_undriven() const { return type_ == DriveType::NONE; }
+	bool is_none() const { return type_ == DriveType::NONE; }
 	bool is_constant() const { return type_ == DriveType::CONSTANT; }
 	bool is_wire() const { return type_ == DriveType::WIRE; }
 	bool is_port() const { return type_ == DriveType::PORT; }