diff --git a/importer/pkginfo.go b/importer/pkginfo.go
index 0b098785..b0d099f3 100644
--- a/importer/pkginfo.go
+++ b/importer/pkginfo.go
@@ -9,7 +9,6 @@ package importer
 import (
 	"fmt"
 	"go/ast"
-	"go/token"
 
 	"code.google.com/p/go.tools/go/exact"
 	"code.google.com/p/go.tools/go/types"
@@ -96,119 +95,3 @@ func (info *PackageInfo) TypeCaseVar(cc *ast.CaseClause) *types.Var {
 	}
 	return nil
 }
-
-var (
-	tEface      = new(types.Interface)
-	tComplex64  = types.Typ[types.Complex64]
-	tComplex128 = types.Typ[types.Complex128]
-	tFloat32    = types.Typ[types.Float32]
-	tFloat64    = types.Typ[types.Float64]
-)
-
-// BuiltinCallSignature returns a new Signature describing the
-// effective type of a builtin operator for the particular call e.
-//
-// This requires ad-hoc typing rules for all variadic (append, print,
-// println) and polymorphic (append, copy, delete, close) built-ins.
-// This logic could be part of the typechecker, and should arguably
-// be moved there and made accessible via an additional types.Context
-// callback.
-//
-func (info *PackageInfo) BuiltinCallSignature(e *ast.CallExpr) *types.Signature {
-	var params []*types.Var
-	var isVariadic bool
-
-	switch builtin := unparen(e.Fun).(*ast.Ident).Name; builtin {
-	case "append":
-		var t0, t1 types.Type
-		t0 = info.TypeOf(e) // infer arg[0] type from result type
-		if e.Ellipsis != 0 {
-			// append(tslice, tslice...) []T
-			// append(byteslice, "foo"...) []byte
-			t1 = info.TypeOf(e.Args[1]) // no conversion
-		} else {
-			// append([]T, x, y, z) []T
-			t1 = t0.Underlying()
-			isVariadic = true
-		}
-		params = append(params,
-			types.NewVar(token.NoPos, nil, "", t0),
-			types.NewVar(token.NoPos, nil, "", t1))
-
-	case "print", "println": // print{,ln}(any, ...)
-		// Note, args may have any type, not necessarily tEface.
-		var params []*types.Var
-		for _, arg := range e.Args {
-			params = append(params, types.NewVar(token.NoPos, nil, "", info.TypeOf(arg)))
-		}
-
-	case "close":
-		params = append(params, types.NewVar(token.NoPos, nil, "", info.TypeOf(e.Args[0])))
-
-	case "copy":
-		// copy([]T, []T) int
-		// Infer arg types from each other.  Sleazy.
-		var st *types.Slice
-		if t, ok := info.TypeOf(e.Args[0]).Underlying().(*types.Slice); ok {
-			st = t
-		} else if t, ok := info.TypeOf(e.Args[1]).Underlying().(*types.Slice); ok {
-			st = t
-		} else {
-			panic("cannot infer types in call to copy()")
-		}
-		stvar := types.NewVar(token.NoPos, nil, "", st)
-		params = append(params, stvar, stvar)
-
-	case "delete":
-		// delete(map[K]V, K)
-		tmap := info.TypeOf(e.Args[0])
-		tkey := tmap.Underlying().(*types.Map).Key()
-		params = append(params,
-			types.NewVar(token.NoPos, nil, "", tmap),
-			types.NewVar(token.NoPos, nil, "", tkey))
-
-	case "len", "cap":
-		params = append(params, types.NewVar(token.NoPos, nil, "", info.TypeOf(e.Args[0])))
-
-	case "real", "imag":
-		// Reverse conversion to "complex" case below.
-		var argType types.Type
-		switch info.TypeOf(e).(*types.Basic).Kind() {
-		case types.UntypedFloat:
-			argType = types.Typ[types.UntypedComplex]
-		case types.Float64:
-			argType = tComplex128
-		case types.Float32:
-			argType = tComplex64
-		default:
-			unreachable()
-		}
-		params = append(params, types.NewVar(token.NoPos, nil, "", argType))
-
-	case "complex":
-		var argType types.Type
-		switch info.TypeOf(e).(*types.Basic).Kind() {
-		case types.UntypedComplex:
-			argType = types.Typ[types.UntypedFloat]
-		case types.Complex128:
-			argType = tFloat64
-		case types.Complex64:
-			argType = tFloat32
-		default:
-			unreachable()
-		}
-		v := types.NewVar(token.NoPos, nil, "", argType)
-		params = append(params, v, v)
-
-	case "panic":
-		params = append(params, types.NewVar(token.NoPos, nil, "", tEface))
-
-	case "recover":
-		// no params
-
-	default:
-		panic("unknown builtin: " + builtin)
-	}
-
-	return types.NewSignature(nil, nil, types.NewTuple(params...), nil, isVariadic)
-}
diff --git a/ssa/builder.go b/ssa/builder.go
index a23b8777..ff544a68 100644
--- a/ssa/builder.go
+++ b/ssa/builder.go
@@ -936,7 +936,7 @@ func (b *builder) setCall(fn *Function, e *ast.CallExpr, c *CallCommon) {
 	// Then append the other actual parameters.
 	sig, _ := fn.Pkg.typeOf(e.Fun).Underlying().(*types.Signature)
 	if sig == nil {
-		sig = fn.Pkg.info.BuiltinCallSignature(e)
+		panic(fmt.Sprintf("no signature for call of %s", e.Fun))
 	}
 	c.Args = b.emitCallArgs(fn, sig, e, c.Args)
 }