diff --git a/src/cmd/go/build.go b/src/cmd/go/build.go
index e201f29e766..a3916cae28c 100644
--- a/src/cmd/go/build.go
+++ b/src/cmd/go/build.go
@@ -93,6 +93,10 @@ and test commands:
 		a list of build tags to consider satisfied during the build.
 		For more information about build tags, see the description of
 		build constraints in the documentation for the go/build package.
+	-toolexec 'cmd args'
+		a program to use to invoke toolchain programs like 5a, 5g, and 5l.
+		For example, instead of running 5g, the go command will run
+		'cmd args /path/to/5g <arguments for 5g>'.
 
 The list flags accept a space-separated list of strings. To embed spaces
 in an element in the list, surround it with either single or double quotes.
@@ -131,6 +135,7 @@ var buildCcflags []string    // -ccflags flag
 var buildLdflags []string    // -ldflags flag
 var buildGccgoflags []string // -gccgoflags flag
 var buildRace bool           // -race flag
+var buildToolExec []string   // -toolexec flag
 
 var buildContext = build.Default
 var buildToolchain toolchain = noToolchain{}
@@ -184,6 +189,7 @@ func addBuildFlags(cmd *Command) {
 	cmd.Flag.Var((*stringsFlag)(&buildContext.BuildTags), "tags", "")
 	cmd.Flag.Var(buildCompiler{}, "compiler", "")
 	cmd.Flag.BoolVar(&buildRace, "race", false, "")
+	cmd.Flag.Var((*stringsFlag)(&buildToolExec), "toolexec", "")
 }
 
 func addBuildFlagsNX(cmd *Command) {
@@ -1229,6 +1235,7 @@ func (b *builder) copyFile(a *action, dst, src string, perm os.FileMode) error {
 //	go tool cover -mode=b.coverMode -var="varName" -o dst.go src.go
 func (b *builder) cover(a *action, dst, src string, perm os.FileMode, varName string) error {
 	return b.run(a.objdir, "cover "+a.p.ImportPath, nil,
+		buildToolExec,
 		tool("cover"),
 		"-mode", a.p.coverMode,
 		"-var", varName,
@@ -1657,7 +1664,7 @@ func (gcToolchain) gc(b *builder, p *Package, archive, obj string, asmhdr bool,
 		gcargs = append(gcargs, "-installsuffix", buildContext.InstallSuffix)
 	}
 
-	args := stringList(tool(archChar+"g"), "-o", ofile, "-trimpath", b.work, buildGcflags, gcargs, "-D", p.localPrefix, importArgs)
+	args := stringList(buildToolExec, tool(archChar+"g"), "-o", ofile, "-trimpath", b.work, buildGcflags, gcargs, "-D", p.localPrefix, importArgs)
 	if ofile == archive {
 		args = append(args, "-pack")
 	}
@@ -1676,7 +1683,7 @@ func (gcToolchain) asm(b *builder, p *Package, obj, ofile, sfile string) error {
 	// Add -I pkg/GOOS_GOARCH so #include "textflag.h" works in .s files.
 	inc := filepath.Join(goroot, "pkg", fmt.Sprintf("%s_%s", goos, goarch))
 	sfile = mkAbs(p.Dir, sfile)
-	return b.run(p.Dir, p.ImportPath, nil, tool(archChar+"a"), "-trimpath", b.work, "-I", obj, "-I", inc, "-o", ofile, "-D", "GOOS_"+goos, "-D", "GOARCH_"+goarch, sfile)
+	return b.run(p.Dir, p.ImportPath, nil, stringList(buildToolExec, tool(archChar+"a"), "-trimpath", b.work, "-I", obj, "-I", inc, "-o", ofile, "-D", "GOOS_"+goos, "-D", "GOARCH_"+goarch, sfile))
 }
 
 func (gcToolchain) pkgpath(basedir string, p *Package) string {
@@ -1715,7 +1722,7 @@ func (gcToolchain) pack(b *builder, p *Package, objDir, afile string, ofiles []s
 
 	// Need actual pack.
 	cmdline[0] = tool("pack")
-	return b.run(p.Dir, p.ImportPath, nil, cmdline)
+	return b.run(p.Dir, p.ImportPath, nil, buildToolExec, cmdline)
 }
 
 func packInternal(b *builder, afile string, ofiles []string) error {
@@ -1823,7 +1830,7 @@ func (gcToolchain) ld(b *builder, p *Package, out string, allactions []*action,
 		}
 	}
 	ldflags = append(ldflags, buildLdflags...)
-	return b.run(".", p.ImportPath, nil, tool(archChar+"l"), "-o", out, importArgs, ldflags, mainpkg)
+	return b.run(".", p.ImportPath, nil, stringList(buildToolExec, tool(archChar+"l"), "-o", out, importArgs, ldflags, mainpkg))
 }
 
 func (gcToolchain) cc(b *builder, p *Package, objdir, ofile, cfile string) error {
@@ -2212,7 +2219,7 @@ func (b *builder) cgo(p *Package, cgoExe, obj string, pcCFLAGS, pcLDFLAGS, gccfi
 		}
 		objExt = "o"
 	}
-	if err := b.run(p.Dir, p.ImportPath, cgoenv, cgoExe, "-objdir", obj, cgoflags, "--", cgoCPPFLAGS, cgoexeCFLAGS, p.CgoFiles); err != nil {
+	if err := b.run(p.Dir, p.ImportPath, cgoenv, buildToolExec, cgoExe, "-objdir", obj, cgoflags, "--", cgoCPPFLAGS, cgoexeCFLAGS, p.CgoFiles); err != nil {
 		return nil, nil, err
 	}
 	outGo = append(outGo, gofiles...)
@@ -2344,7 +2351,7 @@ func (b *builder) cgo(p *Package, cgoExe, obj string, pcCFLAGS, pcLDFLAGS, gccfi
 	if p.Standard && p.ImportPath == "runtime/cgo" {
 		cgoflags = append(cgoflags, "-dynlinker") // record path to dynamic linker
 	}
-	if err := b.run(p.Dir, p.ImportPath, nil, cgoExe, "-objdir", obj, "-dynpackage", p.Name, "-dynimport", dynobj, "-dynout", importGo, cgoflags); err != nil {
+	if err := b.run(p.Dir, p.ImportPath, nil, buildToolExec, cgoExe, "-objdir", obj, "-dynpackage", p.Name, "-dynimport", dynobj, "-dynout", importGo, cgoflags); err != nil {
 		return nil, nil, err
 	}
 	outGo = append(outGo, importGo)
diff --git a/src/cmd/go/doc.go b/src/cmd/go/doc.go
index fac6ba8fe26..9b642019454 100644
--- a/src/cmd/go/doc.go
+++ b/src/cmd/go/doc.go
@@ -112,6 +112,10 @@ and test commands:
 		a list of build tags to consider satisfied during the build.
 		For more information about build tags, see the description of
 		build constraints in the documentation for the go/build package.
+	-toolexec 'cmd args'
+		a program to use to invoke toolchain programs like 5a, 5g, and 5l.
+		For example, instead of running 5g, the go command will run
+		'cmd args /path/to/5g <arguments for 5g>'.
 
 The list flags accept a space-separated list of strings. To embed spaces
 in an element in the list, surround it with either single or double quotes.
diff --git a/src/cmd/go/fix.go b/src/cmd/go/fix.go
index 8736cce3e2a..858feab24b7 100644
--- a/src/cmd/go/fix.go
+++ b/src/cmd/go/fix.go
@@ -25,6 +25,6 @@ func runFix(cmd *Command, args []string) {
 		// Use pkg.gofiles instead of pkg.Dir so that
 		// the command only applies to this package,
 		// not to packages in subdirectories.
-		run(stringList(tool("fix"), relPaths(pkg.allgofiles)))
+		run(stringList(buildToolExec, tool("fix"), relPaths(pkg.allgofiles)))
 	}
 }
diff --git a/src/cmd/go/get.go b/src/cmd/go/get.go
index 50e0ca93bf4..01ca4b2acdf 100644
--- a/src/cmd/go/get.go
+++ b/src/cmd/go/get.go
@@ -223,7 +223,7 @@ func download(arg string, stk *importStack, getTestDeps bool) {
 	// due to wildcard expansion.
 	for _, p := range pkgs {
 		if *getFix {
-			run(stringList(tool("fix"), relPaths(p.allgofiles)))
+			run(buildToolExec, stringList(tool("fix"), relPaths(p.allgofiles)))
 
 			// The imports might have changed, so reload again.
 			p = reloadPackage(arg, stk)
diff --git a/src/cmd/go/vet.go b/src/cmd/go/vet.go
index 02ff54b2ac8..2634536afff 100644
--- a/src/cmd/go/vet.go
+++ b/src/cmd/go/vet.go
@@ -46,5 +46,5 @@ func runVetFiles(p *Package, files []string) {
 	for i := range files {
 		files[i] = filepath.Join(p.Dir, files[i])
 	}
-	run(tool("vet"), relPaths(files))
+	run(buildToolExec, tool("vet"), relPaths(files))
 }