diff --git a/bootstrap/command.go b/bootstrap/command.go
index 4e0b40e..301f0e3 100644
--- a/bootstrap/command.go
+++ b/bootstrap/command.go
@@ -20,7 +20,6 @@ import (
 	"fmt"
 	"io"
 	"os"
-	"path/filepath"
 	"runtime"
 	"runtime/debug"
 	"runtime/pprof"
@@ -64,7 +63,7 @@ func RunBlueprint(args Args, stopBefore StopBefore, ctx *blueprint.Context, conf
 	}
 
 	if args.Cpuprofile != "" {
-		f, err := os.Create(joinPath(ctx.SrcDir(), args.Cpuprofile))
+		f, err := os.Create(blueprint.JoinPath(ctx.SrcDir(), args.Cpuprofile))
 		if err != nil {
 			return nil, fmt.Errorf("error opening cpuprofile: %s", err)
 		}
@@ -74,7 +73,7 @@ func RunBlueprint(args Args, stopBefore StopBefore, ctx *blueprint.Context, conf
 	}
 
 	if args.TraceFile != "" {
-		f, err := os.Create(joinPath(ctx.SrcDir(), args.TraceFile))
+		f, err := os.Create(blueprint.JoinPath(ctx.SrcDir(), args.TraceFile))
 		if err != nil {
 			return nil, fmt.Errorf("error opening trace: %s", err)
 		}
@@ -159,12 +158,12 @@ func RunBlueprint(args Args, stopBefore StopBefore, ctx *blueprint.Context, conf
 	ctx.BeginEvent("write_files")
 	defer ctx.EndEvent("write_files")
 	if args.EmptyNinjaFile {
-		if err := os.WriteFile(joinPath(ctx.SrcDir(), args.OutFile), []byte(nil), blueprint.OutFilePermissions); err != nil {
+		if err := os.WriteFile(blueprint.JoinPath(ctx.SrcDir(), args.OutFile), []byte(nil), blueprint.OutFilePermissions); err != nil {
 			return nil, fmt.Errorf("error writing empty Ninja file: %s", err)
 		}
 		out = io.Discard.(blueprint.StringWriterWriter)
 	} else {
-		f, err := os.OpenFile(joinPath(ctx.SrcDir(), args.OutFile), os.O_WRONLY|os.O_CREATE|os.O_TRUNC, blueprint.OutFilePermissions)
+		f, err := os.OpenFile(blueprint.JoinPath(ctx.SrcDir(), args.OutFile), os.O_WRONLY|os.O_CREATE|os.O_TRUNC, blueprint.OutFilePermissions)
 		if err != nil {
 			return nil, fmt.Errorf("error opening Ninja file: %s", err)
 		}
@@ -195,7 +194,7 @@ func RunBlueprint(args Args, stopBefore StopBefore, ctx *blueprint.Context, conf
 	}
 
 	if args.Memprofile != "" {
-		f, err := os.Create(joinPath(ctx.SrcDir(), args.Memprofile))
+		f, err := os.Create(blueprint.JoinPath(ctx.SrcDir(), args.Memprofile))
 		if err != nil {
 			return nil, fmt.Errorf("error opening memprofile: %s", err)
 		}
@@ -223,10 +222,3 @@ func fatalErrors(errs []error) error {
 
 	return errors.New("fatal errors encountered")
 }
-
-func joinPath(base, path string) string {
-	if filepath.IsAbs(path) {
-		return path
-	}
-	return filepath.Join(base, path)
-}
diff --git a/bootstrap/glob.go b/bootstrap/glob.go
index 9054341..4611cef 100644
--- a/bootstrap/glob.go
+++ b/bootstrap/glob.go
@@ -196,7 +196,7 @@ func (s *GlobSingleton) GenerateBuildActions(ctx blueprint.SingletonContext) {
 		// We don't need to write the depfile because we're guaranteed that ninja
 		// will run the command at least once (to record it into the ninja_log), so
 		// the depfile will be loaded from that execution.
-		absoluteFileListFile := joinPath(s.SrcDir, fileListFile)
+		absoluteFileListFile := blueprint.JoinPath(s.SrcDir, fileListFile)
 		err := pathtools.WriteFileIfChanged(absoluteFileListFile, globs.FileList(), 0666)
 		if err != nil {
 			panic(fmt.Errorf("error writing %s: %s", fileListFile, err))
@@ -217,7 +217,7 @@ func WriteBuildGlobsNinjaFile(glob *GlobSingleton, config interface{}) error {
 	}
 
 	const outFilePermissions = 0666
-	err := ioutil.WriteFile(joinPath(glob.SrcDir, glob.GlobFile), buffer, outFilePermissions)
+	err := ioutil.WriteFile(blueprint.JoinPath(glob.SrcDir, glob.GlobFile), buffer, outFilePermissions)
 	if err != nil {
 		return fmt.Errorf("error writing %s: %s", glob.GlobFile, err)
 	}
diff --git a/context.go b/context.go
index 00dd7d8..46f2985 100644
--- a/context.go
+++ b/context.go
@@ -4544,9 +4544,9 @@ func (c *Context) writeAllModuleActions(nw *ninjaWriter, shardNinja bool, ninjaF
 			wg.Add(1)
 			go func(file string, batchModules []*moduleInfo) {
 				defer wg.Done()
-				f, err := os.OpenFile(filepath.Join(c.SrcDir(), file), os.O_WRONLY|os.O_CREATE|os.O_TRUNC, OutFilePermissions)
+				f, err := os.OpenFile(JoinPath(c.SrcDir(), file), os.O_WRONLY|os.O_CREATE|os.O_TRUNC, OutFilePermissions)
 				if err != nil {
-					errorCh <- fmt.Errorf("error opening Ninja file: %s", err)
+					errorCh <- fmt.Errorf("error opening Ninja file shard: %s", err)
 					return
 				}
 				defer func() {
@@ -5259,3 +5259,10 @@ func (pi *PackageIncludes) matchesIncludeTags(ctx *Context) (bool, error) {
 	}
 	return true, nil
 }
+
+func JoinPath(base, path string) string {
+	if filepath.IsAbs(path) {
+		return path
+	}
+	return filepath.Join(base, path)
+}