diff --git a/sdk/core/azure-core/CHANGELOG.md b/sdk/core/azure-core/CHANGELOG.md
index f40443f06..e6e17c49f 100644
--- a/sdk/core/azure-core/CHANGELOG.md
+++ b/sdk/core/azure-core/CHANGELOG.md
@@ -6,11 +6,13 @@
 
 - Request logs to now include the `accept-range`, `content-range`, `range`, `WWW-Authenticate`, `x-ms-date`, `x-ms-error-code`, `x-ms-range`, and `x-ms-version` headers.
 - Added default constructor, `Parse()`, and equality comparison operators to `Azure::Core::Uuid`.
+- Added an `Azure::Core::ResourceIdentifier` type.
 
 ### Breaking Changes
 
 ### Bugs Fixed
 
+- Throw `std::invalid_argument` if the value of `TimeFractionFormat` enum passed in to `DateTime::ToString()` is invalid.
 - `Azure::Core::Uuid::ToString()` is now `const`.
 
 ### Other Changes
@@ -20,7 +22,6 @@
 ### Features Added
 
 - Added new constructor for `Azure::Core::Context` that takes a `std::chrono::system_clock::time_point` deadline. This enables creating a new context directly with a deadline.
-- Added an `Azure::Core::ResourceIdentifier` type.
  
 ### Breaking Changes
 
diff --git a/sdk/core/azure-core/src/datetime.cpp b/sdk/core/azure-core/src/datetime.cpp
index e9d0c0d8d..0869ae57c 100644
--- a/sdk/core/azure-core/src/datetime.cpp
+++ b/sdk/core/azure-core/src/datetime.cpp
@@ -12,6 +12,7 @@
 #include <limits>
 #include <sstream>
 #include <stdexcept>
+#include <type_traits>
 
 using namespace Azure;
 
@@ -863,6 +864,20 @@ std::string DateTime::ToString(DateFormat format, TimeFractionFormat fractionFor
         "Unrecognized date format (" + std::to_string(static_cast<int64_t>(format)) + ").");
   }
 
+  switch (fractionFormat)
+  {
+    case TimeFractionFormat::DropTrailingZeros:
+    case TimeFractionFormat::AllDigits:
+    case TimeFractionFormat::Truncate:
+      break;
+    default:
+      throw std::invalid_argument(
+          "Unrecognized time fraction format ("
+          + std::to_string(
+              static_cast<std::underlying_type<TimeFractionFormat>::type>(fractionFormat))
+          + ").");
+  }
+
   ThrowIfUnsupportedYear();
 
   int16_t year = 1;
diff --git a/sdk/core/azure-core/test/ut/datetime_test.cpp b/sdk/core/azure-core/test/ut/datetime_test.cpp
index cb057debb..7f2ea7d85 100644
--- a/sdk/core/azure-core/test/ut/datetime_test.cpp
+++ b/sdk/core/azure-core/test/ut/datetime_test.cpp
@@ -494,6 +494,13 @@ TEST(DateTime, ToStringInvalid)
   EXPECT_THROW(
       dt.ToString(DateTime::DateFormat::Rfc1123, static_cast<DateTime::TimeFractionFormat>(3)),
       std::invalid_argument);
+
+  EXPECT_THROW(
+      dt.ToString(DateTime::DateFormat::Rfc3339, static_cast<DateTime::TimeFractionFormat>(3)),
+      std::invalid_argument);
+  EXPECT_THROW(
+      dt.ToString(DateTime::DateFormat::Rfc3339, static_cast<DateTime::TimeFractionFormat>(-3)),
+      std::invalid_argument);
 }
 
 TEST(DateTime, ParseTimeInvalid2)