diff --git a/internal/evaluator/map.go b/internal/evaluator/map.go
index 405bf6f..fd3aa46 100644
--- a/internal/evaluator/map.go
+++ b/internal/evaluator/map.go
@@ -15,6 +15,9 @@
 package evaluator
 
 import (
+	"fmt"
+	"strconv"
+
 	"github.com/bufbuild/protovalidate-go/internal/errors"
 	"google.golang.org/protobuf/reflect/protoreflect"
 )
@@ -32,7 +35,7 @@ func (m kvPairs) Evaluate(val protoreflect.Value, failFast bool) (err error) {
 	val.Map().Range(func(key protoreflect.MapKey, value protoreflect.Value) bool {
 		evalErr := m.evalPairs(key, value, failFast)
 		if evalErr != nil {
-			errors.PrefixErrorPaths(evalErr, "[%#v]", key.Interface())
+			errors.PrefixErrorPaths(evalErr, "[%s]", m.formatKey(key.Interface()))
 		}
 		ok, err = errors.Merge(err, evalErr, failFast)
 		return ok
@@ -57,4 +60,13 @@ func (m kvPairs) Tautology() bool {
 		m.ValueConstraints.Tautology()
 }
 
+func (m kvPairs) formatKey(key any) string {
+	switch k := key.(type) {
+	case string:
+		return strconv.Quote(k)
+	default:
+		return fmt.Sprintf("%v", key)
+	}
+}
+
 var _ evaluator = kvPairs{}
diff --git a/internal/evaluator/map_test.go b/internal/evaluator/map_test.go
new file mode 100644
index 0000000..da36366
--- /dev/null
+++ b/internal/evaluator/map_test.go
@@ -0,0 +1,54 @@
+package evaluator
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestFormatKey(t *testing.T) {
+	t.Parallel()
+	tests := []struct {
+		key      any
+		expected string
+	}{
+		{
+			key:      int32(32),
+			expected: "32",
+		},
+		{
+			key:      int64(64),
+			expected: "64",
+		},
+		{
+			key:      uint32(32),
+			expected: "32",
+		},
+		{
+			key:      uint32(64),
+			expected: "64",
+		},
+		{
+			key:      true,
+			expected: "true",
+		},
+		{
+			key:      false,
+			expected: "false",
+		},
+		{
+			key:      `"foobar"`,
+			expected: `"\"foobar\""`,
+		},
+	}
+
+	kv := kvPairs{}
+	for _, tc := range tests {
+		test := tc
+		t.Run(test.expected, func(t *testing.T) {
+			t.Parallel()
+			actual := kv.formatKey(test.key)
+			assert.Equal(t, test.expected, actual)
+		})
+	}
+}