diff --git a/sandbox.go b/sandbox.go
index c4a865d..2050832 100644
--- a/sandbox.go
+++ b/sandbox.go
@@ -370,7 +370,7 @@
 			return nil, fmt.Errorf("error creating temp directory: %v", err)
 		}
 		defer os.RemoveAll(goPath)
-		cmd.Env = append(cmd.Env, "GO111MODULE=on", "GOPROXY=https://proxy.golang.org")
+		cmd.Env = append(cmd.Env, "GO111MODULE=on", "GOPROXY="+playgroundGoproxy())
 	} else {
 		goPath = os.Getenv("GOPATH")                 // contains old code.google.com/p/go-tour, etc
 		cmd.Env = append(cmd.Env, "GO111MODULE=off") // in case it becomes on by default later
@@ -451,13 +451,24 @@
 		// these packages to still run, so the Dockerfile adds these packages
 		// at this name in $GOPATH. Any snippets using this old name wouldn't
 		// have expected (or been able to use) third-party packages anyway,
-		// so disabling modules and proxy.golang.org fetches is acceptable.
+		// so disabling modules and proxy fetches is acceptable.
 		return false
 	}
 	v, _ := strconv.ParseBool(os.Getenv("ALLOW_PLAY_MODULE_DOWNLOADS"))
 	return v
 }
 
+// playgroundGoproxy returns the GOPROXY environment config the playground should use.
+// It is fetched from the environment variable PLAY_GOPROXY. A missing or empty
+// value for PLAY_GOPROXY returns the default value of https://proxy.golang.org.
+func playgroundGoproxy() string {
+	proxypath := os.Getenv("PLAY_GOPROXY")
+	if proxypath != "" {
+		return proxypath
+	}
+	return "https://proxy.golang.org"
+}
+
 func (s *server) healthCheck() error {
 	resp, err := compileAndRun(&request{Body: healthProg})
 	if err != nil {
diff --git a/server_test.go b/server_test.go
index 9cc19da..773a093 100644
--- a/server_test.go
+++ b/server_test.go
@@ -272,5 +272,36 @@
 			t.Errorf("%d. allow = %v; want %v; files:\n%s", i, got, tt.want, filesAsString(files))
 		}
 	}
+}
 
+func TestPlaygroundGoproxy(t *testing.T) {
+	const envKey = "PLAY_GOPROXY"
+	defer os.Setenv(envKey, os.Getenv(envKey))
+
+	tests := []struct {
+		name string
+		env  string
+		want string
+	}{
+		{name: "missing", env: "", want: "https://proxy.golang.org"},
+		{name: "set_to_default", env: "https://proxy.golang.org", want: "https://proxy.golang.org"},
+		{name: "changed", env: "https://company.intranet", want: "https://company.intranet"},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if tt.env != "" {
+				if err := os.Setenv(envKey, tt.env); err != nil {
+					t.Errorf("unable to set environment variable for test: %s", err)
+				}
+			} else {
+				if err := os.Unsetenv(envKey); err != nil {
+					t.Errorf("unable to unset environment variable for test: %s", err)
+				}
+			}
+			got := playgroundGoproxy()
+			if got != tt.want {
+				t.Errorf("playgroundGoproxy = %s; want %s; env: %s", got, tt.want, tt.env)
+			}
+		})
+	}
 }
diff --git a/vet.go b/vet.go
index 32edeca..a9cae12 100644
--- a/vet.go
+++ b/vet.go
@@ -60,7 +60,7 @@
 	if modules {
 		cmd.Env = append(cmd.Env,
 			"GO111MODULE=on",
-			"GOPROXY=https://proxy.golang.org",
+			"GOPROXY="+playgroundGoproxy(),
 		)
 	}
 	out, err := cmd.CombinedOutput()