diff --git a/src/libfmt_macros/lib.rs b/src/libfmt_macros/lib.rs
index 32ae878909f..da440cdd72f 100644
--- a/src/libfmt_macros/lib.rs
+++ b/src/libfmt_macros/lib.rs
@@ -72,6 +72,15 @@ pub enum Position<'a> {
     ArgumentNamed(&'a str),
 }
 
+impl Position<'_> {
+    pub fn index(&self) -> Option<usize> {
+        match self {
+            ArgumentIs(i) | ArgumentImplicitlyIs(i) => Some(*i),
+            _ => None,
+        }
+    }
+}
+
 /// Enum of alignments which are supported.
 #[derive(Copy, Clone, PartialEq)]
 pub enum Alignment {
diff --git a/src/libsyntax_ext/format.rs b/src/libsyntax_ext/format.rs
index 61722ba5516..0613c78e495 100644
--- a/src/libsyntax_ext/format.rs
+++ b/src/libsyntax_ext/format.rs
@@ -493,7 +493,10 @@ fn build_piece(&mut self,
 
                 let fill = arg.format.fill.unwrap_or(' ');
 
-                if *arg != simple_arg || fill != ' ' {
+                let pos_simple =
+                    arg.position.index() == simple_arg.position.index();
+
+                if !pos_simple || arg.format != simple_arg.format || fill != ' ' {
                     self.all_pieces_simple = false;
                 }