diff --git a/compiler-rt/lib/scudo/standalone/string_utils.h b/compiler-rt/lib/scudo/standalone/string_utils.h
--- a/compiler-rt/lib/scudo/standalone/string_utils.h
+++ b/compiler-rt/lib/scudo/standalone/string_utils.h
@@ -28,6 +28,7 @@
   void append(const char *Format, va_list Args);
   void append(const char *Format, ...) FORMAT(2, 3);
   void output() const { outputRaw(String.data()); }
+  void reserve(size_t Size) { String.reserve(Size + 1); }
 
 private:
   Vector<char> String;
diff --git a/compiler-rt/lib/scudo/standalone/tests/strings_test.cpp b/compiler-rt/lib/scudo/standalone/tests/strings_test.cpp
--- a/compiler-rt/lib/scudo/standalone/tests/strings_test.cpp
+++ b/compiler-rt/lib/scudo/standalone/tests/strings_test.cpp
@@ -43,9 +43,11 @@
 }
 
 TEST(ScudoStringsTest, ClearLarge) {
+  constexpr char appendString[] = "123";
   scudo::ScopedString Str;
+  Str.reserve(sizeof(appendString) * 10000);
   for (int i = 0; i < 10000; ++i)
-    Str.append("123");
+    Str.append(appendString);
   Str.clear();
   EXPECT_EQ(0ul, Str.length());
   EXPECT_EQ('\0', *Str.data());
@@ -76,6 +78,7 @@
   // of it with variations of append. The expectation is for nothing to crash.
   const scudo::uptr PageSize = scudo::getPageSizeCached();
   scudo::ScopedString Str;
+  Str.reserve(2 * PageSize);
   Str.clear();
   fillString(Str, 2 * PageSize);
   Str.clear();