diff --git a/llvm/lib/Support/Z3Solver.cpp b/llvm/lib/Support/Z3Solver.cpp
index 5a34ff160f6cf42..9aece099b06295a 100644
--- a/llvm/lib/Support/Z3Solver.cpp
+++ b/llvm/lib/Support/Z3Solver.cpp
@@ -19,6 +19,7 @@ using namespace llvm;
 #include "llvm/ADT/Twine.h"
 
 #include <set>
+#include <unordered_map>
 
 #include <z3.h>