diff --git a/lang/funcs/filesystem.go b/lang/funcs/filesystem.go
index ed8a9d1bc8..7dfc905875 100644
--- a/lang/funcs/filesystem.go
+++ b/lang/funcs/filesystem.go
@@ -92,7 +92,7 @@ func MakeTemplateFileFunc(baseDir string, funcsCb func() map[string]function.Fun
 
 	renderTmpl := func(expr hcl.Expression, varsVal cty.Value) (cty.Value, error) {
 		if varsTy := varsVal.Type(); !(varsTy.IsMapType() || varsTy.IsObjectType()) {
-			return cty.DynamicVal, function.NewArgErrorf(2, "invalid vars value: must be a map") // or an object, but we don't strongly distinguish these most of the time
+			return cty.DynamicVal, function.NewArgErrorf(1, "invalid vars value: must be a map") // or an object, but we don't strongly distinguish these most of the time
 		}
 
 		ctx := &hcl.EvalContext{
@@ -105,7 +105,7 @@ func MakeTemplateFileFunc(baseDir string, funcsCb func() map[string]function.Fun
 		for _, traversal := range expr.Variables() {
 			root := traversal.RootName()
 			if _, ok := ctx.Variables[root]; !ok {
-				return cty.DynamicVal, function.NewArgErrorf(2, "vars map does not contain key %q, referenced at %s", root, traversal[0].SourceRange())
+				return cty.DynamicVal, function.NewArgErrorf(1, "vars map does not contain key %q, referenced at %s", root, traversal[0].SourceRange())
 			}
 		}
 
diff --git a/lang/funcs/filesystem_test.go b/lang/funcs/filesystem_test.go
index c8e68d3606..d64e78423b 100644
--- a/lang/funcs/filesystem_test.go
+++ b/lang/funcs/filesystem_test.go
@@ -159,6 +159,12 @@ func TestTemplateFile(t *testing.T) {
 		t.Run(fmt.Sprintf("TemplateFile(%#v, %#v)", test.Path, test.Vars), func(t *testing.T) {
 			got, err := templateFileFn.Call([]cty.Value{test.Path, test.Vars})
 
+			if argErr, ok := err.(function.ArgError); ok {
+				if argErr.Index < 0 || argErr.Index > 1 {
+					t.Errorf("ArgError index %d is out of range for templatefile (must be 0 or 1)", argErr.Index)
+				}
+			}
+
 			if test.Err {
 				if err == nil {
 					t.Fatal("succeeded; want error")