diff --git a/src/cmd/go/internal/envcmd/env.go b/src/cmd/go/internal/envcmd/env.go
index c62a41901e..2e3e9d3973 100644
--- a/src/cmd/go/internal/envcmd/env.go
+++ b/src/cmd/go/internal/envcmd/env.go
@@ -73,11 +73,16 @@ func MkEnv() []cfg.EnvVar {
 		env = append(env, cfg.EnvVar{Name: "GO386", Value: cfg.GO386})
 	}
 
-	cmd := b.GccCmd(".", "")
-	env = append(env, cfg.EnvVar{Name: "CC", Value: cmd[0]})
-	env = append(env, cfg.EnvVar{Name: "GOGCCFLAGS", Value: strings.Join(cmd[3:], " ")})
-	cmd = b.GxxCmd(".", "")
-	env = append(env, cfg.EnvVar{Name: "CXX", Value: cmd[0]})
+	cc := cfg.DefaultCC
+	if env := strings.Fields(os.Getenv("CC")); len(env) > 0 {
+		cc = env[0]
+	}
+	cxx := cfg.DefaultCXX
+	if env := strings.Fields(os.Getenv("CXX")); len(env) > 0 {
+		cxx = env[0]
+	}
+	env = append(env, cfg.EnvVar{Name: "CC", Value: cc})
+	env = append(env, cfg.EnvVar{Name: "CXX", Value: cxx})
 
 	if cfg.BuildContext.CgoEnabled {
 		env = append(env, cfg.EnvVar{Name: "CGO_ENABLED", Value: "1"})
@@ -102,19 +107,45 @@ func ExtraEnvVars() []cfg.EnvVar {
 	var b work.Builder
 	b.Init()
 	cppflags, cflags, cxxflags, fflags, ldflags := b.CFlags(&load.Package{})
+	cmd := b.GccCmd(".", "")
 	return []cfg.EnvVar{
+		// Note: Update the switch in runEnv below when adding to this list.
 		{Name: "CGO_CFLAGS", Value: strings.Join(cflags, " ")},
 		{Name: "CGO_CPPFLAGS", Value: strings.Join(cppflags, " ")},
 		{Name: "CGO_CXXFLAGS", Value: strings.Join(cxxflags, " ")},
 		{Name: "CGO_FFLAGS", Value: strings.Join(fflags, " ")},
 		{Name: "CGO_LDFLAGS", Value: strings.Join(ldflags, " ")},
 		{Name: "PKG_CONFIG", Value: b.PkgconfigCmd()},
+		{Name: "GOGCCFLAGS", Value: strings.Join(cmd[3:], " ")},
 	}
 }
 
 func runEnv(cmd *base.Command, args []string) {
 	env := cfg.CmdEnv
-	env = append(env, ExtraEnvVars()...)
+
+	// Do we need to call ExtraEnvVars, which is a bit expensive?
+	// Only if we're listing all environment variables ("go env")
+	// or the variables being requested are in the extra list.
+	needExtra := true
+	if len(args) > 0 {
+		needExtra = false
+		for _, arg := range args {
+			switch arg {
+			case "CGO_CFLAGS",
+				"CGO_CPPFLAGS",
+				"CGO_CXXFLAGS",
+				"CGO_FFLAGS",
+				"CGO_LDFLAGS",
+				"PKG_CONFIG",
+				"GOGCCFLAGS":
+				needExtra = true
+			}
+		}
+	}
+	if needExtra {
+		env = append(env, ExtraEnvVars()...)
+	}
+
 	if len(args) > 0 {
 		if *envJson {
 			var es []cfg.EnvVar
diff --git a/src/cmd/go/internal/work/exec.go b/src/cmd/go/internal/work/exec.go
index 385882b454..b652b71b4a 100644
--- a/src/cmd/go/internal/work/exec.go
+++ b/src/cmd/go/internal/work/exec.go
@@ -1232,30 +1232,39 @@ func (b *Builder) gccld(p *load.Package, objdir, out string, flags []string, obj
 	return b.run(p.Dir, p.ImportPath, nil, cmd, "-o", out, objs, flags)
 }
 
+// Grab these before main helpfully overwrites them.
+var (
+	origCC  = os.Getenv("CC")
+	origCXX = os.Getenv("CXX")
+)
+
 // gccCmd returns a gcc command line prefix
 // defaultCC is defined in zdefaultcc.go, written by cmd/dist.
 func (b *Builder) GccCmd(incdir, workdir string) []string {
-	return b.compilerCmd("CC", cfg.DefaultCC, incdir, workdir)
+	return b.compilerCmd(origCC, cfg.DefaultCC, incdir, workdir)
 }
 
 // gxxCmd returns a g++ command line prefix
 // defaultCXX is defined in zdefaultcc.go, written by cmd/dist.
 func (b *Builder) GxxCmd(incdir, workdir string) []string {
-	return b.compilerCmd("CXX", cfg.DefaultCXX, incdir, workdir)
+	return b.compilerCmd(origCXX, cfg.DefaultCXX, incdir, workdir)
 }
 
 // gfortranCmd returns a gfortran command line prefix.
 func (b *Builder) gfortranCmd(incdir, workdir string) []string {
-	return b.compilerCmd("FC", "gfortran", incdir, workdir)
+	return b.compilerCmd(os.Getenv("FC"), "gfortran", incdir, workdir)
 }
 
 // compilerCmd returns a command line prefix for the given environment
 // variable and using the default command when the variable is empty.
-func (b *Builder) compilerCmd(envvar, defcmd, incdir, workdir string) []string {
+func (b *Builder) compilerCmd(envValue, defcmd, incdir, workdir string) []string {
 	// NOTE: env.go's mkEnv knows that the first three
 	// strings returned are "gcc", "-I", incdir (and cuts them off).
 
-	compiler := envList(envvar, defcmd)
+	if envValue == "" {
+		envValue = defcmd
+	}
+	compiler := strings.Fields(envValue)
 	a := []string{compiler[0], "-I", incdir}
 	a = append(a, compiler[1:]...)