diff --git a/fpd.y b/fpd.y
index c91366b..5130c37 100644
--- a/fpd.y
+++ b/fpd.y
@@ -128,6 +128,7 @@ static struct obj *new_obj(enum obj_type type)
 	obj->type = type;
 	obj->frame = curr_frame;
 	obj->next = NULL;
+	obj->lineno = lineno;
 	return obj;
 }
 
diff --git a/gui_tool.c b/gui_tool.c
index 754230d..a37fc7d 100644
--- a/gui_tool.c
+++ b/gui_tool.c
@@ -413,6 +413,7 @@ static int end_new_pad(struct inst *from, struct inst *to)
 	obj->u.pad.other = inst_get_vec(to);
 	obj->u.pad.name = stralloc("?");
 	obj->u.pad.rounded = 0;
+	obj->u.pad.type = pt_normal;
 	return 1;
 }
 
diff --git a/inst.c b/inst.c
index 2bb7a7f..3e99157 100644
--- a/inst.c
+++ b/inst.c
@@ -799,7 +799,8 @@ int inst_pad(struct obj *obj, const char *name, struct coord a, struct coord b)
 	struct inst *inst;
 
 	inst = add_inst(obj->u.pad.rounded ? &rpad_ops : &pad_ops,
-	    obj->u.pad.type == pt_bare ? ip_pad_bare : ip_pad, a);
+	    obj->u.pad.type == pt_normal || obj->u.pad.type == pt_bare ?
+	    ip_pad_copper : ip_pad_special, a);
 	inst->obj = obj;
 	inst->u.pad.name = stralloc(name);
 	inst->u.pad.other = b;
@@ -1105,7 +1106,8 @@ struct bbox inst_get_bbox(void)
 static void cleanup_inst(enum inst_prio prio, const struct inst *inst)
 {
 	switch (prio) {
-	case ip_pad:
+	case ip_pad_copper:
+	case ip_pad_special:
 		free(inst->u.pad.name);
 		break;
 	default:
diff --git a/inst.h b/inst.h
index a6f7cd5..6f302c4 100644
--- a/inst.h
+++ b/inst.h
@@ -38,8 +38,8 @@ struct bbox {
 
 enum inst_prio {
 	ip_frame,	/* frames have their own selection */
-	ip_pad_bare,	/* pads also accept clicks inside */
-	ip_pad,		/* pads with solder mask on top of those without */
+	ip_pad_copper,	/* pads also accept clicks inside; pads with copper */
+	ip_pad_special,	/* pads with only solder paste or mask, on top */
 	ip_circ,	/* circles don't overlap easily */
 	ip_arc,		/* arc are like circles, just shorter */
 	ip_rect,	/* rectangles have plenty of sides */
@@ -132,7 +132,7 @@ extern struct bbox active_frame_bbox;
  * frame being instantiated - we need to export this one for meas.c, so that
  * measurement scan update the root frame's bounding box.
  */
-extern	struct inst *curr_frame;
+extern struct inst *curr_frame;
 
 /*
  * @@@ Note that we over-generalize a bit here: the only item that ever ends up
diff --git a/kicad.c b/kicad.c
index 2f058e0..5e78422 100644
--- a/kicad.c
+++ b/kicad.c
@@ -148,8 +148,8 @@ static void kicad_arc(FILE *file, const struct inst *inst)
 static void kicad_inst(FILE *file, enum inst_prio prio, const struct inst *inst)
 {
 	switch (prio) {
-	case ip_pad:
-	case ip_pad_bare:
+	case ip_pad_copper:
+	case ip_pad_special:
 		kicad_pad(file, inst);
 		break;
 	case ip_line:
diff --git a/layer.c b/layer.c
index 2d47f45..75b0a47 100644
--- a/layer.c
+++ b/layer.c
@@ -10,12 +10,34 @@
  * (at your option) any later version.
  */
 
+/*
+ * We don't reject solder paste pads that don't cover anything yet.
+ * That way, things can be constructed step by step without getting blue
+ * screens all the time.
+ */
+
 
 #include <stdlib.h>
 
+#include "error.h"
+#include "overlap.h"
+#include "inst.h"
+#include "obj.h"
 #include "layer.h"
 
 
+/*
+ * Shorthands for the layers we use in a general sense.
+ */
+
+#define LAYER_COPPER	(1 << layer_top)
+#define LAYER_PASTE	(1 << layer_paste_top)
+#define LAYER_MASK	(1 << layer_mask_top)
+
+
+/* ----- Conversion between pad types and layer sets ----------------------- */
+
+
 layer_type pad_type_to_layers(enum pad_type type)
 {
 	layer_type layers = 0;
@@ -54,3 +76,70 @@ enum pad_type layers_to_pad_type(layer_type layers)
 		abort();
 	}
 }
+
+
+/* ----- Refine layers after instantiation --------------------------------- */
+
+
+static int refine_overlapping(struct inst *copper, struct inst *other)
+{
+	if (other->u.pad.layers & LAYER_PASTE) {
+		copper->u.pad.layers &= ~LAYER_PASTE;
+		if (!inside(other, copper)) {
+			fail("solder paste without copper underneath "
+			    "(\"%s\" line %d, \"%s\" line %d)",
+			    copper->u.pad.name, copper->obj->lineno,
+			    other->u.pad.name, other->obj->lineno);
+			instantiation_error = other->obj;
+			return 0;
+		}
+	}
+	if (other->u.pad.layers & LAYER_MASK)
+		copper->u.pad.layers &= ~LAYER_MASK;
+	return 1;
+}
+
+
+static int refine_copper(const struct pkg *pkg_copper, struct inst *copper)
+{
+	const struct pkg *pkg;
+	struct inst *other;
+
+	for (pkg = pkgs; pkg; pkg = pkg->next) {
+		/*
+		 * Pads in distinct packages can happily coexist.
+		 */
+		if (pkg != pkgs && pkg_copper != pkgs && pkg_copper != pkg)
+			continue;
+		for (other = pkg->insts[ip_pad_copper]; other;
+		    other = other->next)
+			if (copper != other && overlap(copper, other)) {
+				fail("overlapping copper pads "
+				    "(\"%s\" line %d, \"%s\" line %d)",
+				    copper->u.pad.name, copper->obj->lineno,
+				    other->u.pad.name, other->obj->lineno);
+				instantiation_error = copper->obj;
+				return 0;
+			}
+		for (other = pkg->insts[ip_pad_special]; other;
+		    other = other->next)
+			if (overlap(copper, other))
+				if (!refine_overlapping(copper, other))
+					return 0;
+	}
+	return 1;
+}
+
+
+int refine_layers(void)
+{
+	const struct pkg *pkg;
+	struct inst *copper;
+
+	for (pkg = pkgs; pkg; pkg = pkg->next)
+		for (copper = pkg->insts[ip_pad_copper]; copper;
+		    copper = copper->next)
+			if (!refine_copper(pkg, copper))
+				return 0;
+	return 1;
+}
diff --git a/layer.h b/layer.h
index 90b1399..adc0dc2 100644
--- a/layer.h
+++ b/layer.h
@@ -61,15 +61,6 @@ enum pad_type {
 };
 
 
-/*
- * Shorthands for the layers we use in a general sense.
- */
-
-#define	LAYER_COPPER	(1 << layer_top)
-#define	LAYER_PASTE	(1 << layer_paste_top)
-#define	LAYER_MASK	(1 << layer_mask_top)
-
-
 /*
  * pad_type_to_layers returns the initial set of layers. This set can then be
  * modified by overlaying other pads. For display purposes, we translate back
@@ -82,4 +73,6 @@ enum pad_type {
 layer_type pad_type_to_layers(enum pad_type type);
 enum pad_type layers_to_pad_type(layer_type layers);
 
+int refine_layers(void);
+
 #endif /* !LAYER_H */
diff --git a/obj.c b/obj.c
index 3fa66b1..abc70ff 100644
--- a/obj.c
+++ b/obj.c
@@ -20,6 +20,7 @@
 #include "expr.h"
 #include "meas.h"
 #include "inst.h"
+#include "layer.h"
 #include "delete.h"
 #include "obj.h"
 
@@ -303,6 +304,8 @@ int instantiate(void)
 	instantiation_error = NULL;
 	reset_all_loops();
 	ok = generate_frame(root_frame, zero, NULL, NULL, 1);
+	if (ok)
+		ok = refine_layers();
 	if (ok)
 		ok = instantiate_meas();
 	if (ok)
diff --git a/overlap.c b/overlap.c
index fb9cdca..3a8787a 100644
--- a/overlap.c
+++ b/overlap.c
@@ -127,7 +127,7 @@ static int do_rect(const struct inst *next, const struct shape *other,
 		},
 		.max = {
 			.x = x+w,
-			.y = y+w,
+			.y = y+h,
 		},
 	};
 
@@ -160,9 +160,9 @@ static int test_overlap(const struct inst *a, const struct inst *b,
 		    do_circle(b, other, min.x+r, min.y+r, r);
 	} else {
 		r = h/2;
-		return do_circle(b, other, min.x+r, max.y+r, r) ||
+		return do_circle(b, other, min.x+r, min.y+r, r) ||
 		    do_rect(b, other, min.x+r, min.y, w-2*r, h) ||
-		    do_circle(b, other, min.x-r, min.y+r, r);
+		    do_circle(b, other, max.x-r, min.y+r, r);
 	}
 }
 
diff --git a/postscript.c b/postscript.c
index 9a04d67..d2abb5e 100644
--- a/postscript.c
+++ b/postscript.c
@@ -477,8 +477,8 @@ static void ps_foreground(FILE *file, enum inst_prio prio,
      const struct inst *inst, double zoom)
 {
 	switch (prio) {
-	case ip_pad:
-	case ip_pad_bare:
+	case ip_pad_copper:
+	case ip_pad_special:
 		if (inst->obj->u.pad.rounded)
 			ps_rpad(file, inst, active_params.show_pad_names);
 		else