diff --git a/cmd/txtpbfmt/fmt.go b/cmd/txtpbfmt/fmt.go
index 57ac928..0ca1ff1 100644
--- a/cmd/txtpbfmt/fmt.go
+++ b/cmd/txtpbfmt/fmt.go
@@ -46,6 +46,19 @@ func contentForLogging(content []byte) string {
 	return res
 }
 
+// parserLog satisfies parser.Logger. Note that glog only exposes Errorf as a
+// top-level function, and not as a method.
+type parserLog struct {
+	log.Verbose
+}
+
+func (l parserLog) Errorf(format string, args ...interface{}) {
+	log.Errorf(format, args...)
+}
+func (l parserLog) InfoLevel() bool {
+	return bool(l.Verbose)
+}
+
 func main() {
 	flag.Parse()
 	paths := flag.Args()
@@ -72,6 +85,7 @@ func main() {
 			ExpandAllChildren:        *expandAllChildren,
 			SkipAllColons:            *skipAllColons,
 			AllowTripleQuotedStrings: *allowTripleQuotedStrings,
+			Logger:                   parserLog{log.V(2)},
 		})
 		if err != nil {
 			errorf("parser.Format for path %v with content %q returned err %v", path, contentForLogging(content), err)
diff --git a/go.sum b/go.sum
index b4c4a5a..73e288e 100644
--- a/go.sum
+++ b/go.sum
@@ -6,4 +6,5 @@ github.com/kylelemons/godebug v1.1.0 h1:RPNrshWIDI6G2gRW9EHilWtl7Z6Sb1BR0xunSBf0
 github.com/kylelemons/godebug v1.1.0/go.mod h1:9/0rRGxNHcop5bhtWyNeEfOS8JIWk580+fNqagV/RAw=
 github.com/mitchellh/go-wordwrap v1.0.1 h1:TLuKupo69TCn6TQSyGxwI1EblZZEsQ0vMlAFQflz0v0=
 github.com/mitchellh/go-wordwrap v1.0.1/go.mod h1:R62XHJLzvMFRBbcrT7m7WgmE1eOyTSsCt+hzestvNj0=
+golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543 h1:E7g+9GITq07hpfrRu66IVDexMakfv52eLZ2CXBWiKr4=
 golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
diff --git a/parser/parser.go b/parser/parser.go
index bdad37c..f33ac31 100644
--- a/parser/parser.go
+++ b/parser/parser.go
@@ -16,7 +16,6 @@ import (
 	"strconv"
 	"strings"
 
-	log "github.com/golang/glog"
 	"github.com/mitchellh/go-wordwrap"
 	"github.com/protocolbuffers/txtpbfmt/ast"
 	"github.com/protocolbuffers/txtpbfmt/unquote"
@@ -78,6 +77,36 @@ type Config struct {
 
 	// Use single quotes around strings that contain double but not single quotes.
 	SmartQuotes bool
+
+	// Logger enables logging when it is non-nil.
+	Logger Logger
+}
+
+func (c *Config) errorf(format string, args ...interface{}) {
+	if c.Logger != nil {
+		c.Logger.Errorf(format, args...)
+	}
+}
+func (c *Config) infof(format string, args ...interface{}) {
+	if c.Logger != nil {
+		c.Logger.Infof(format, args...)
+	}
+}
+func (c *Config) infoLevel() bool {
+	return c.Logger != nil && c.Logger.InfoLevel()
+}
+
+// Logger is a small glog-like interface.
+type Logger interface {
+	// Infof is used for informative messages, for testing or debugging.
+	Infof(format string, args ...interface{})
+
+	// Errorf is used for non-fatal errors, such as invalid meta comments.
+	Errorf(format string, args ...interface{})
+
+	// InfoLevel reports whether Infof messages will be logged.
+	// When it returns false, the caller can avoid constructing its log messages.
+	InfoLevel() bool
 }
 
 // RootName contains a constant that can be used to identify the root of all Nodes.
@@ -119,7 +148,6 @@ type parser struct {
 	in     []byte
 	index  int
 	length int
-	log    log.Verbose
 	// Maps the index of '{' characters on 'in' that have the matching '}' on
 	// the same line to 'true'.
 	bracketSameLine map[int]bool
@@ -163,7 +191,7 @@ func Format(in []byte) ([]byte, error) {
 func FormatWithConfig(in []byte, c Config) ([]byte, error) {
 	addMetaCommentsToConfig(in, &c)
 	if c.Disable {
-		log.Infoln("Ignored file with 'disable' comment.")
+		c.infof("Ignored file with 'disable' comment.")
 		return in, nil
 	}
 	nodes, err := parseWithMetaCommentConfig(in, c)
@@ -322,9 +350,9 @@ func parseWithMetaCommentConfig(in []byte, c Config) ([]*ast.Node, error) {
 	if err != nil {
 		return nil, err
 	}
-	if p.log {
-		p.log.Infof("p.in: %q", string(p.in))
-		p.log.Infof("p.length: %v", p.length)
+	if p.config.infoLevel() {
+		p.config.infof("p.in: %q", string(p.in))
+		p.config.infof("p.length: %v", p.length)
 	}
 	// Although unnamed nodes aren't strictly allowed, some formats represent a
 	// list of protos as a list of unnamed top-level nodes.
@@ -375,21 +403,21 @@ func addMetaCommentsToConfig(in []byte, c *Config) {
 	if metaComments["sort_repeated_fields_by_content"] {
 		c.SortRepeatedFieldsByContent = true
 	}
-	for _, sf := range getMetaCommentStringValues("sort_repeated_fields_by_subfield", metaComments) {
+	for _, sf := range getMetaCommentStringValues(c, "sort_repeated_fields_by_subfield", metaComments) {
 		c.SortRepeatedFieldsBySubfield = append(c.SortRepeatedFieldsBySubfield, sf)
 	}
 	if metaComments["wrap_html_strings"] {
 		c.WrapHTMLStrings = true
 	}
-	setMetaCommentIntValue("wrap_strings_at_column", metaComments, &c.WrapStringsAtColumn)
+	setMetaCommentIntValue(c, "wrap_strings_at_column", metaComments, &c.WrapStringsAtColumn)
 }
 
 // For a MetaComment in the form comment_name=<int> set *int to the value. Will not change
 // the *int if the comment name isn't present.
-func setMetaCommentIntValue(name string, metaComments map[string]bool, value *int) {
+func setMetaCommentIntValue(c *Config, name string, metaComments map[string]bool, value *int) {
 	for mc := range metaComments {
 		if strings.HasPrefix(mc, fmt.Sprintf("%s ", name)) {
-			log.Errorf("format should be %s=<int>, got: %s", name, mc)
+			c.errorf("format should be %s=<int>, got: %s", name, mc)
 			return
 		}
 		prefix := fmt.Sprintf("%s=", name)
@@ -398,7 +426,7 @@ func setMetaCommentIntValue(name string, metaComments map[string]bool, value *in
 			var err error
 			i, err := strconv.Atoi(strings.TrimSpace(intStr))
 			if err != nil {
-				log.Errorf("error parsing %s value %q (skipping): %v", name, intStr, err)
+				c.errorf("error parsing %s value %q (skipping): %v", name, intStr, err)
 				return
 			}
 			*value = i
@@ -407,11 +435,11 @@ func setMetaCommentIntValue(name string, metaComments map[string]bool, value *in
 }
 
 // For a MetaComment in the form comment_name=<string> returns the strings.
-func getMetaCommentStringValues(name string, metaComments map[string]bool) []string {
+func getMetaCommentStringValues(c *Config, name string, metaComments map[string]bool) []string {
 	var vs []string
 	for mc := range metaComments {
 		if strings.HasPrefix(mc, fmt.Sprintf("%s ", name)) {
-			log.Errorf("format should be %s=<string>, got: %s", name, mc)
+			c.errorf("format should be %s=<string>, got: %s", name, mc)
 			continue
 		}
 		prefix := fmt.Sprintf("%s=", name)
@@ -439,7 +467,6 @@ func newParser(in []byte, c Config) (*parser, error) {
 		in:              in,
 		index:           0,
 		length:          len(in),
-		log:             log.V(2),
 		bracketSameLine: bracketSameLine,
 		config:          c,
 		line:            1,
@@ -572,8 +599,8 @@ func (p *parser) parse(isRoot bool) (result []*ast.Node, endPos ast.Position, er
 
 		// Handle blank lines.
 		if blankLines > 1 {
-			if p.log {
-				p.log.Infof("blankLines: %v", blankLines)
+			if p.config.infoLevel() {
+				p.config.infof("blankLines: %v", blankLines)
 			}
 			comments = append([]string{""}, comments...)
 		}
@@ -610,8 +637,8 @@ func (p *parser) parse(isRoot bool) (result []*ast.Node, endPos ast.Position, er
 			Start:       startPos,
 			PreComments: comments,
 		}
-		if p.log {
-			p.log.Infof("PreComments: %q", strings.Join(nd.PreComments, "\n"))
+		if p.config.infoLevel() {
+			p.config.infof("PreComments: %q", strings.Join(nd.PreComments, "\n"))
 		}
 
 		// Skip white-space other than '\n', which is handled below.
@@ -653,8 +680,8 @@ func (p *parser) parse(isRoot bool) (result []*ast.Node, endPos ast.Position, er
 				return nil, ast.Position{}, fmt.Errorf("Failed to find a FieldName at %s", p.errorContext())
 			}
 		}
-		if p.log {
-			p.log.Infof("name: %q", nd.Name)
+		if p.config.infoLevel() {
+			p.config.infof("name: %q", nd.Name)
 		}
 		// Skip separator.
 		_, _ = p.skipWhiteSpaceAndReadComments(true /* multiLine */)
@@ -756,8 +783,8 @@ func (p *parser) parse(isRoot bool) (result []*ast.Node, endPos ast.Position, er
 				return nil, ast.Position{}, err
 			}
 		}
-		if p.log && p.index < p.length {
-			p.log.Infof("p.in[p.index]: %q", string(p.in[p.index]))
+		if p.config.infoLevel() && p.index < p.length {
+			p.config.infof("p.in[p.index]: %q", string(p.in[p.index]))
 		}
 		res = append(res, nd)
 	}
@@ -839,10 +866,10 @@ func (p *parser) skipWhiteSpaceAndReadComments(multiLine bool) ([]string, int) {
 		}
 	}
 	sep := p.advance(i)
-	if p.log {
-		p.log.Infof("sep: %q\np.index: %v", string(sep), p.index)
+	if p.config.infoLevel() {
+		p.config.infof("sep: %q\np.index: %v", string(sep), p.index)
 		if p.index < p.length {
-			p.log.Infof("p.in[p.index]: %q", string(p.in[p.index]))
+			p.config.infof("p.in[p.index]: %q", string(p.in[p.index]))
 		}
 	}
 	return comments, blankLines
@@ -940,8 +967,8 @@ func (p *parser) readValues() ([]*ast.Value, error) {
 		vl := p.advance(i)
 		values = append(values, p.populateValue(vl, nil))
 	}
-	if p.log {
-		p.log.Infof("values: %v", values)
+	if p.config.infoLevel() {
+		p.config.infof("values: %v", values)
 	}
 	return values, nil
 }
@@ -974,8 +1001,8 @@ func (p *parser) readTripleQuotedString() (*ast.Value, error) {
 }
 
 func (p *parser) populateValue(vl string, preComments []string) *ast.Value {
-	if p.log {
-		p.log.Infof("value: %q", vl)
+	if p.config.infoLevel() {
+		p.config.infof("value: %q", vl)
 	}
 	return &ast.Value{
 		Value:         vl,
@@ -986,8 +1013,8 @@ func (p *parser) populateValue(vl string, preComments []string) *ast.Value {
 
 func (p *parser) readInlineComment() string {
 	inlineComment, _ := p.skipWhiteSpaceAndReadComments(false /* multiLine */)
-	if p.log {
-		p.log.Infof("inlineComment: %q", strings.Join(inlineComment, "\n"))
+	if p.config.infoLevel() {
+		p.config.infof("inlineComment: %q", strings.Join(inlineComment, "\n"))
 	}
 	if len(inlineComment) > 0 {
 		return inlineComment[0]
@@ -1124,7 +1151,7 @@ func wrapLines(nd *ast.Node, depth int, c Config) {
 
 	str, err := unquote.Raw(nd)
 	if err != nil {
-		log.Errorf("skipping string wrapping on node %q (error unquoting string): %v", nd.Name, err)
+		c.errorf("skipping string wrapping on node %q (error unquoting string): %v", nd.Name, err)
 		return
 	}