diff --git a/logger.go b/logger.go
index e1f024a72..1b59cd5a4 100644
--- a/logger.go
+++ b/logger.go
@@ -6,6 +6,7 @@ import (
 	"log"
 	"strconv"
 	"strings"
+	"sync"
 )
 
 type StdLogger interface {
@@ -32,12 +33,32 @@ func (n nopLogger) Debug(_ string, _ ...LogField) {}
 
 type testLogger struct {
 	capture bytes.Buffer
+	mu      sync.Mutex
 }
 
-func (l *testLogger) Print(v ...interface{})                 { fmt.Fprint(&l.capture, v...) }
-func (l *testLogger) Printf(format string, v ...interface{}) { fmt.Fprintf(&l.capture, format, v...) }
-func (l *testLogger) Println(v ...interface{})               { fmt.Fprintln(&l.capture, v...) }
-func (l *testLogger) String() string                         { return l.capture.String() }
+func (l *testLogger) Print(v ...interface{}) {
+	l.mu.Lock()
+	defer l.mu.Unlock()
+	fmt.Fprint(&l.capture, v...)
+}
+
+func (l *testLogger) Printf(format string, v ...interface{}) {
+	l.mu.Lock()
+	defer l.mu.Unlock()
+	fmt.Fprintf(&l.capture, format, v...)
+}
+
+func (l *testLogger) Println(v ...interface{}) {
+	l.mu.Lock()
+	defer l.mu.Unlock()
+	fmt.Fprintln(&l.capture, v...)
+}
+
+func (l *testLogger) String() string {
+	l.mu.Lock()
+	defer l.mu.Unlock()
+	return l.capture.String()
+}
 
 type defaultLogger struct{}