diff --git a/cue/binop.go b/cue/binop.go
index 663bd68..c2e8787 100644
--- a/cue/binop.go
+++ b/cue/binop.go
@@ -222,7 +222,7 @@
 		return other
 	}
 	src = mkBin(ctx, src.Pos(), op, x, other)
-	return ctx.mkErr(src, "binary operation on non-ground top value")
+	return ctx.mkErr(src, codeIncomplete, "binary operation on (incomplete) top value")
 }
 
 func (x *basicType) binOp(ctx *context, src source, op op, other evaluated) evaluated {
@@ -681,7 +681,7 @@
 		switch op {
 		case opUnify:
 			if x.b != y.b {
-				return ctx.mkErr(x, "failed to unify: %v != %v", x.b, y.b)
+				return ctx.mkErr(x, "conflicting values: %v != %v", x.b, y.b)
 			}
 			return x
 		case opLand:
@@ -711,7 +711,7 @@
 			str := other.strValue()
 			if x.str != str {
 				src := mkBin(ctx, src.Pos(), op, x, other)
-				return ctx.mkErr(src, "failed to unify: %v != %v", x.str, str)
+				return ctx.mkErr(src, "conflicting values: %v != %v", x.str, str)
 			}
 			return x
 		case opLss, opLeq, opEql, opNeq, opGeq, opGtr:
@@ -754,7 +754,7 @@
 		switch op {
 		case opUnify:
 			if !bytes.Equal(x.b, b) {
-				return ctx.mkErr(x, "failed to unify: %v != %v", x.b, b)
+				return ctx.mkErr(x, "conflicting values: %v != %v", x.b, b)
 			}
 			return x
 		case opLss, opLeq, opEql, opNeq, opGeq, opGtr:
@@ -863,7 +863,7 @@
 		case opUnify:
 			if x.v.Cmp(&y.v) != 0 {
 				src = mkBin(ctx, src.Pos(), op, x, other)
-				return ctx.mkErr(src, "cannot unify numbers %v and %v", x.strValue(), y.strValue())
+				return ctx.mkErr(src, "conflicting values: %v != %v", x.strValue(), y.strValue())
 			}
 			if k != x.k {
 				n.v = x.v
@@ -1126,7 +1126,7 @@
 		n, m := len(x.params.arcs), len(y.params.arcs)
 		if n != m {
 			src = mkBin(ctx, src.Pos(), op, x, other)
-			return ctx.mkErr(src, "number of params of params should match in unification (%d != %d)", n, m)
+			return ctx.mkErr(src, "number of params should match (%d != %d)", n, m)
 		}
 		arcs := make([]arc, len(x.arcs))
 		lambda := &lambdaExpr{binSrc(src.Pos(), op, x, other), &params{arcs}, nil}
diff --git a/cue/resolve_test.go b/cue/resolve_test.go
index e645a6a..605b486 100644
--- a/cue/resolve_test.go
+++ b/cue/resolve_test.go
@@ -247,7 +247,7 @@
 			e: true
 			e: !true
 			`,
-		out: "<0>{t: true, f: false, e: _|_(true:failed to unify: true != false)}",
+		out: "<0>{t: true, f: false, e: _|_(true:conflicting values: true != false)}",
 	}, {
 		desc: "boolean arithmetic",
 		in: `
@@ -258,7 +258,7 @@
 			e: true & true
 			f: true & false
 			`,
-		out: "<0>{a: true, b: true, c: false, d: true, e: true, f: _|_(true:failed to unify: true != false)}",
+		out: "<0>{a: true, b: true, c: false, d: true, e: true, f: _|_(true:conflicting values: true != false)}",
 	}, {
 		desc: "basic type",
 		in: `
@@ -520,9 +520,9 @@
 			x: x + 1
 		`,
 		out: `<0>{` +
-			`a: _|_((210 & 200):cannot unify numbers 210 and 200), ` +
-			`b: _|_((210 & 200):cannot unify numbers 210 and 200), ` +
-			`x: _|_((100 & 101):cannot unify numbers 100 and 101)}`,
+			`a: _|_((210 & 200):conflicting values: 210 != 200), ` +
+			`b: _|_((210 & 200):conflicting values: 210 != 200), ` +
+			`x: _|_((100 & 101):conflicting values: 100 != 101)}`,
 		// TODO: find a way to mark error in data.
 	}}
 	rewriteHelper(t, testCases, evalPartial)
@@ -877,7 +877,7 @@
 			`i2: 3, ` +
 			`t0: [<3>{a: 8}], ` +
 			`t1: [, ...int], ` +
-			`e0: _|_(([<4>{},<4>{}] & [<5>{}]):incompatible list lengths: cannot unify numbers 2 and 1), ` +
+			`e0: _|_(([<4>{},<4>{}] & [<5>{}]):incompatible list lengths: conflicting values: 2 != 1), ` +
 			`e1: _|_(([, ...int] & [, ...float]):incompatible list types: unsupported op &(int, float): )` +
 			`}`,
 	}, {
@@ -1355,7 +1355,7 @@
 			`a3: <3>{a: _|_((=~"oo" & "bar"):"bar" does not match =~"oo"), b: =~"oo", c: =~"fo"}, ` +
 			`o1: <4>{a: string, b: string, c: "bar"}, ` +
 			`o2: <5>{a: "foo", b: string, c: "bar"}, ` +
-			`o3: <6>{a: _|_((builtin:or ([<7>.b,<7>.c]) & "foo"):empty disjunction: failed to unify: baz != foo), b: "baz", c: "bar"}}`,
+			`o3: <6>{a: _|_((builtin:or ([<7>.b,<7>.c]) & "foo"):empty disjunction: conflicting values: baz != foo), b: "baz", c: "bar"}}`,
 	}, {
 		desc: "self-reference cycles conflicts with strings",
 		in: `
@@ -1365,7 +1365,7 @@
 			}
 			a x: "hey"
 		`,
-		out: `<0>{a: <1>{x: _|_(("hey!?" & "hey"):failed to unify: hey!? != hey), y: "hey!"}}`,
+		out: `<0>{a: <1>{x: _|_(("hey!?" & "hey"):conflicting values: hey!? != hey), y: "hey!"}}`,
 	}, {
 		desc: "resolved self-reference cycles with disjunctions",
 		in: `
@@ -1463,11 +1463,11 @@
 			`xd5: 10, ` +
 			`xd3: 6, ` +
 
-			`xe1: _|_((6 & 7):cannot unify numbers 6 and 7), ` +
-			`xe2: _|_((6 & 7):cannot unify numbers 6 and 7), ` +
-			`xe4: _|_((6 & 7):cannot unify numbers 6 and 7), ` +
-			`xe5: _|_((6 & 7):cannot unify numbers 6 and 7), ` +
-			`xe3: _|_((6 & 7):cannot unify numbers 6 and 7), ` +
+			`xe1: _|_((6 & 7):conflicting values: 6 != 7), ` +
+			`xe2: _|_((6 & 7):conflicting values: 6 != 7), ` +
+			`xe4: _|_((6 & 7):conflicting values: 6 != 7), ` +
+			`xe5: _|_((6 & 7):conflicting values: 6 != 7), ` +
+			`xe3: _|_((6 & 7):conflicting values: 6 != 7), ` +
 
 			`xf1: 8, ` +
 			`xf2: 8, ` +
@@ -1553,11 +1553,11 @@
 			`xd5: 10, ` +
 			`xd3: 6, ` +
 
-			`xe1: _|_((6 & 7):cannot unify numbers 6 and 7), ` +
-			`xe2: _|_((6 & 7):cannot unify numbers 6 and 7), ` +
-			`xe4: _|_((6 & 7):cannot unify numbers 6 and 7), ` +
-			`xe5: _|_((6 & 7):cannot unify numbers 6 and 7), ` +
-			`xe3: _|_((6 & 7):cannot unify numbers 6 and 7), ` +
+			`xe1: _|_((6 & 7):conflicting values: 6 != 7), ` +
+			`xe2: _|_((6 & 7):conflicting values: 6 != 7), ` +
+			`xe4: _|_((6 & 7):conflicting values: 6 != 7), ` +
+			`xe5: _|_((6 & 7):conflicting values: 6 != 7), ` +
+			`xe3: _|_((6 & 7):conflicting values: 6 != 7), ` +
 
 			`z1: (*11 | 13), ` + // 13 is eliminated with evalFull
 			`z2: 10, ` +