diff --git a/kernel/drivertools.cc b/kernel/drivertools.cc
index 9627a467015..31e3c98ffbf 100644
--- a/kernel/drivertools.cc
+++ b/kernel/drivertools.cc
@@ -21,6 +21,30 @@
 
 YOSYS_NAMESPACE_BEGIN
 
+DriveBitWire::DriveBitWire(Wire *wire, int offset) : wire(wire), offset(offset) {}
+
+bool DriveBitWire::operator==(const DriveBitWire &other) const
+{
+    return wire == other.wire && offset == other.offset;
+}
+
+bool DriveBitWire::operator<(const DriveBitWire &other) const
+{
+    if (wire != other.wire)
+        return wire->name < other.wire->name;
+    return offset < other.offset;
+}
+
+unsigned int DriveBitWire::hash() const
+{
+    return mkhash_add(wire->name.hash(), offset);
+}
+
+DriveBitWire::operator SigBit() const
+{
+    return SigBit(wire, offset);
+}
+
 DriveBit::DriveBit(SigBit const &bit)
 {
 	if (bit.is_wire())
diff --git a/kernel/drivertools.h b/kernel/drivertools.h
index 065431fa491..5930101b795 100644
--- a/kernel/drivertools.h
+++ b/kernel/drivertools.h
@@ -57,32 +57,18 @@ enum class DriveType : unsigned char
 
 struct DriveBitWire
 {
-	Wire *wire;
-	int offset;
+    Wire *wire;
+    int offset;
 
-	DriveBitWire(Wire *wire, int offset) : wire(wire), offset(offset) {}
+    DriveBitWire(Wire *wire, int offset);
 
-	bool operator==(const DriveBitWire &other) const
-	{
-		return wire == other.wire && offset == other.offset;
-	}
+    bool operator==(const DriveBitWire &other) const;
 
-	bool operator<(const DriveBitWire &other) const
-	{
-		if (wire != other.wire)
-			return wire->name < other.wire->name;
-		return offset < other.offset;
-	}
+    bool operator<(const DriveBitWire &other) const;
 
-	unsigned int hash() const
-	{
-		return mkhash_add(wire->name.hash(), offset);
-	}
+    unsigned int hash() const;
 
-	operator SigBit() const
-	{
-		return SigBit(wire, offset);
-	}
+    operator SigBit() const;
 };
 
 struct DriveBitPort