Index: lib/Sema/SemaStmt.cpp
===================================================================
--- lib/Sema/SemaStmt.cpp
+++ lib/Sema/SemaStmt.cpp
@@ -2843,6 +2843,7 @@
 
   DiagnoseEmptyStmtBody(ForStmt->getRParenLoc(), B,
                         diag::warn_empty_range_based_for_body);
+  DiagnoseUnusedExprResult(B);
 
   DiagnoseForRangeVariableCopies(*this, ForStmt);
 
Index: test/SemaCXX/warn-unused-result.cpp
===================================================================
--- test/SemaCXX/warn-unused-result.cpp
+++ test/SemaCXX/warn-unused-result.cpp
@@ -206,3 +206,13 @@
   (void)++p;
 }
 } // namespace
+
+namespace PR39837 {
+[[clang::warn_unused_result]] int f(int);
+
+void g() {
+  int a[2];
+  for (int b : a)
+    f(b); // expected-warning {{ignoring return value}}
+}
+} // namespace PR39837