diff --git a/src/testing/testing.go b/src/testing/testing.go
index a44c0a0..d4b108a 100644
--- a/src/testing/testing.go
+++ b/src/testing/testing.go
@@ -384,17 +384,18 @@
 // common holds the elements common between T and B and
 // captures common methods such as Errorf.
 type common struct {
-	mu          sync.RWMutex        // guards this group of fields
-	output      []byte              // Output generated by test or benchmark.
-	w           io.Writer           // For flushToParent.
-	ran         bool                // Test or benchmark (or one of its subtests) was executed.
-	failed      bool                // Test or benchmark has failed.
-	skipped     bool                // Test of benchmark has been skipped.
-	done        bool                // Test is finished and all subtests have completed.
-	helpers     map[string]struct{} // functions to be skipped when writing file/line info
-	cleanups    []func()            // optional functions to be called at the end of the test
-	cleanupName string              // Name of the cleanup function.
-	cleanupPc   []uintptr           // The stack trace at the point where Cleanup was called.
+	mu          sync.RWMutex         // guards this group of fields
+	output      []byte               // Output generated by test or benchmark.
+	w           io.Writer            // For flushToParent.
+	ran         bool                 // Test or benchmark (or one of its subtests) was executed.
+	failed      bool                 // Test or benchmark has failed.
+	skipped     bool                 // Test of benchmark has been skipped.
+	done        bool                 // Test is finished and all subtests have completed.
+	helperPCs   map[uintptr]struct{} // functions to be skipped when writing file/line info
+	helperNames map[string]struct{}  // helperPCs converted to function names
+	cleanups    []func()             // optional functions to be called at the end of the test
+	cleanupName string               // Name of the cleanup function.
+	cleanupPc   []uintptr            // The stack trace at the point where Cleanup was called.
 
 	chatty     *chattyPrinter // A copy of chattyPrinter, if the chatty flag is set.
 	bench      bool           // Whether the current test is a benchmark.
@@ -509,7 +510,7 @@
 			}
 			return prevFrame
 		}
-		if _, ok := c.helpers[frame.Function]; !ok {
+		if _, ok := c.helperNames[frame.Function]; !ok {
 			// Found a frame that wasn't inside a helper function.
 			return frame
 		}
@@ -521,6 +522,14 @@
 // and inserts the final newline if needed and indentation spaces for formatting.
 // This function must be called with c.mu held.
 func (c *common) decorate(s string, skip int) string {
+	// If more helper PCs have been added since we last did the conversion
+	if c.helperNames == nil {
+		c.helperNames = make(map[string]struct{})
+		for pc := range c.helperPCs {
+			c.helperNames[pcToName(pc)] = struct{}{}
+		}
+	}
+
 	frame := c.frameSkip(skip)
 	file := frame.File
 	line := frame.Line
@@ -853,10 +862,19 @@
 func (c *common) Helper() {
 	c.mu.Lock()
 	defer c.mu.Unlock()
-	if c.helpers == nil {
-		c.helpers = make(map[string]struct{})
+	if c.helperPCs == nil {
+		c.helperPCs = make(map[uintptr]struct{})
 	}
-	c.helpers[callerName(1)] = struct{}{}
+	// repeating code from callerName here to save walking a stack frame
+	var pc [1]uintptr
+	n := runtime.Callers(2, pc[:]) // skip runtime.Callers + Helper
+	if n == 0 {
+		panic("testing: zero callers found")
+	}
+	if _, found := c.helperPCs[pc[0]]; !found {
+		c.helperPCs[pc[0]] = struct{}{}
+		c.helperNames = nil // map will be recreated next time it is needed
+	}
 }
 
 // Cleanup registers a function to be called when the test and all its
@@ -995,13 +1013,17 @@
 // callerName gives the function name (qualified with a package path)
 // for the caller after skip frames (where 0 means the current function).
 func callerName(skip int) string {
-	// Make room for the skip PC.
 	var pc [1]uintptr
 	n := runtime.Callers(skip+2, pc[:]) // skip + runtime.Callers + callerName
 	if n == 0 {
 		panic("testing: zero callers found")
 	}
-	frames := runtime.CallersFrames(pc[:n])
+	return pcToName(pc[0])
+}
+
+func pcToName(pc uintptr) string {
+	pcs := []uintptr{pc}
+	frames := runtime.CallersFrames(pcs)
 	frame, _ := frames.Next()
 	return frame.Function
 }