diff --git a/lib/envtemplate/envtemplate.go b/lib/envtemplate/envtemplate.go
index 9d06435bf..6ad779d63 100644
--- a/lib/envtemplate/envtemplate.go
+++ b/lib/envtemplate/envtemplate.go
@@ -5,6 +5,7 @@ import (
 	"io"
 	"log"
 	"os"
+	"regexp"
 	"strings"
 
 	"github.com/valyala/fasttemplate"
@@ -93,14 +94,23 @@ func expand(m map[string]string, s string) (string, error) {
 		return s, nil
 	}
 	result, err := fasttemplate.ExecuteFuncStringWithErr(s, "%{", "}", func(w io.Writer, tag string) (int, error) {
+		if !isValidEnvVarName(tag) {
+			return fmt.Fprintf(w, "%%{%s}", tag)
+		}
 		v, ok := m[tag]
 		if !ok {
 			return 0, fmt.Errorf("missing %q env var", tag)
 		}
-		return w.Write([]byte(v))
+		return fmt.Fprintf(w, "%s", v)
 	})
 	if err != nil {
 		return "", err
 	}
 	return result, nil
 }
+
+func isValidEnvVarName(s string) bool {
+	return envVarNameRegex.MatchString(s)
+}
+
+var envVarNameRegex = regexp.MustCompile("^[a-zA-Z0-9_]+$")
diff --git a/lib/envtemplate/envtemplate_test.go b/lib/envtemplate/envtemplate_test.go
index 375ece944..cdd7b9ab3 100644
--- a/lib/envtemplate/envtemplate_test.go
+++ b/lib/envtemplate/envtemplate_test.go
@@ -24,6 +24,7 @@ func TestExpandTemplates(t *testing.T) {
 	f([]string{"foo=%{bar}", "bar=x"}, []string{"bar=x", "foo=x"})
 	f([]string{"a=x%{b}", "b=y%{c}z%{d}", "c=123", "d=qwe"}, []string{"a=xy123zqwe", "b=y123zqwe", "c=123", "d=qwe"})
 	f([]string{"a=x%{b}y", "b=z%{a}q", "c"}, []string{"a=xzxzxzxz%{a}qyqyqyqy", "b=zxzxzxzx%{b}yqyqyqyq", "c="})
+	f([]string{"a=%{x.y}"}, []string{"a=%{x.y}"})
 }
 
 func TestLookupEnv(t *testing.T) {
@@ -70,6 +71,7 @@ func TestReplaceSuccess(t *testing.T) {
 	f("", "")
 	f("foo", "foo")
 	f("a %{foo}-x", "a bar-x")
+	f("%{foo.bar}", "%{foo.bar}")
 }
 
 func TestReplaceFailure(t *testing.T) {