diff --git a/go/analysis/passes/stdmethods/stdmethods.go b/go/analysis/passes/stdmethods/stdmethods.go
index eead289e..1c18dbc9 100644
--- a/go/analysis/passes/stdmethods/stdmethods.go
+++ b/go/analysis/passes/stdmethods/stdmethods.go
@@ -7,10 +7,7 @@
 package stdmethods
 
 import (
-	"bytes"
-	"fmt"
 	"go/ast"
-	"go/printer"
 	"go/token"
 	"go/types"
 	"strings"
@@ -95,12 +92,12 @@ func run(pass *analysis.Pass) (interface{}, error) {
 		switch n := n.(type) {
 		case *ast.FuncDecl:
 			if n.Recv != nil {
-				canonicalMethod(pass, n.Name, n.Type)
+				canonicalMethod(pass, n.Name)
 			}
 		case *ast.InterfaceType:
 			for _, field := range n.Methods.List {
 				for _, id := range field.Names {
-					canonicalMethod(pass, id, field.Type.(*ast.FuncType))
+					canonicalMethod(pass, id)
 				}
 			}
 		}
@@ -108,7 +105,7 @@ func run(pass *analysis.Pass) (interface{}, error) {
 	return nil, nil
 }
 
-func canonicalMethod(pass *analysis.Pass, id *ast.Ident, t *ast.FuncType) {
+func canonicalMethod(pass *analysis.Pass, id *ast.Ident) {
 	// Expected input/output.
 	expect, ok := canonicalMethods[id.Name]
 	if !ok {
@@ -116,11 +113,9 @@ func canonicalMethod(pass *analysis.Pass, id *ast.Ident, t *ast.FuncType) {
 	}
 
 	// Actual input/output
-	args := typeFlatten(t.Params.List)
-	var results []ast.Expr
-	if t.Results != nil {
-		results = typeFlatten(t.Results.List)
-	}
+	sign := pass.TypesInfo.Defs[id].Type().(*types.Signature)
+	args := sign.Params()
+	results := sign.Results()
 
 	// Do the =s (if any) all match?
 	if !matchParams(pass, expect.args, args, "=") || !matchParams(pass, expect.results, results, "=") {
@@ -136,11 +131,7 @@ func canonicalMethod(pass *analysis.Pass, id *ast.Ident, t *ast.FuncType) {
 			expectFmt += " (" + argjoin(expect.results) + ")"
 		}
 
-		var buf bytes.Buffer
-		if err := printer.Fprint(&buf, pass.Fset, t); err != nil {
-			fmt.Fprintf(&buf, "<%s>", err)
-		}
-		actual := buf.String()
+		actual := sign.String()
 		actual = strings.TrimPrefix(actual, "func")
 		actual = id.Name + actual
 
@@ -159,45 +150,27 @@ func argjoin(x []string) string {
 	return strings.Join(y, ", ")
 }
 
-// Turn parameter list into slice of types
-// (in the ast, types are Exprs).
-// Have to handle f(int, bool) and f(x, y, z int)
-// so not a simple 1-to-1 conversion.
-func typeFlatten(l []*ast.Field) []ast.Expr {
-	var t []ast.Expr
-	for _, f := range l {
-		if len(f.Names) == 0 {
-			t = append(t, f.Type)
-			continue
-		}
-		for range f.Names {
-			t = append(t, f.Type)
-		}
-	}
-	return t
-}
-
 // Does each type in expect with the given prefix match the corresponding type in actual?
-func matchParams(pass *analysis.Pass, expect []string, actual []ast.Expr, prefix string) bool {
+func matchParams(pass *analysis.Pass, expect []string, actual *types.Tuple, prefix string) bool {
 	for i, x := range expect {
 		if !strings.HasPrefix(x, prefix) {
 			continue
 		}
-		if i >= len(actual) {
+		if i >= actual.Len() {
 			return false
 		}
-		if !matchParamType(pass.Fset, pass.Pkg, x, actual[i]) {
+		if !matchParamType(pass.Fset, pass.Pkg, x, actual.At(i).Type()) {
 			return false
 		}
 	}
-	if prefix == "" && len(actual) > len(expect) {
+	if prefix == "" && actual.Len() > len(expect) {
 		return false
 	}
 	return true
 }
 
 // Does this one type match?
-func matchParamType(fset *token.FileSet, pkg *types.Package, expect string, actual ast.Expr) bool {
+func matchParamType(fset *token.FileSet, pkg *types.Package, expect string, actual types.Type) bool {
 	expect = strings.TrimPrefix(expect, "=")
 	// Strip package name if we're in that package.
 	if n := len(pkg.Name()); len(expect) > n && expect[:n] == pkg.Name() && expect[n] == '.' {
@@ -205,7 +178,5 @@ func matchParamType(fset *token.FileSet, pkg *types.Package, expect string, actu
 	}
 
 	// Overkill but easy.
-	var buf bytes.Buffer
-	printer.Fprint(&buf, fset, actual)
-	return buf.String() == expect
+	return actual.String() == expect
 }
diff --git a/go/analysis/passes/stdmethods/testdata/src/a/a.go b/go/analysis/passes/stdmethods/testdata/src/a/a.go
index a007bbfb..829c5b53 100644
--- a/go/analysis/passes/stdmethods/testdata/src/a/a.go
+++ b/go/analysis/passes/stdmethods/testdata/src/a/a.go
@@ -8,7 +8,7 @@ import "fmt"
 
 type T int
 
-func (T) Scan(x fmt.ScanState, c byte) {} // want "should have signature Scan"
+func (T) Scan(x fmt.ScanState, c byte) {} // want `should have signature Scan\(fmt\.ScanState, rune\) error`
 
 func (T) Format(fmt.State, byte) {} // want `should have signature Format\(fmt.State, rune\)`
 
@@ -19,5 +19,5 @@ func (U) Format(byte) {} // no error: first parameter must be fmt.State to trigg
 func (U) GobDecode() {} // want `should have signature GobDecode\(\[\]byte\) error`
 
 type I interface {
-	ReadByte() byte // want "should have signature ReadByte"
+	ReadByte() byte // want `should have signature ReadByte\(\) \(byte, error\)`
 }