diff --git a/python/google/protobuf/internal/message_test.py b/python/google/protobuf/internal/message_test.py
index e42538e1a7..f25cf2ad4b 100755
--- a/python/google/protobuf/internal/message_test.py
+++ b/python/google/protobuf/internal/message_test.py
@@ -382,6 +382,11 @@ class MessageTest(unittest.TestCase):
     message.optional_float = 2.0
     self.assertEqual(str(message), 'optional_float: 2.0\n')
 
+  def testFloatNanPrinting(self, message_module):
+    message = message_module.TestAllTypes()
+    message.optional_float = float('nan')
+    self.assertEqual(str(message), 'optional_float: nan\n')
+
   def testHighPrecisionFloatPrinting(self, message_module):
     msg = message_module.TestAllTypes()
     msg.optional_float = 0.12345678912345678
@@ -389,6 +394,11 @@ class MessageTest(unittest.TestCase):
     msg.ParseFromString(msg.SerializeToString())
     self.assertEqual(old_float, msg.optional_float)
 
+  def testDoubleNanPrinting(self, message_module):
+    message = message_module.TestAllTypes()
+    message.optional_double = float('nan')
+    self.assertEqual(str(message), 'optional_double: nan\n')
+
   def testHighPrecisionDoublePrinting(self, message_module):
     msg = message_module.TestAllTypes()
     msg.optional_double = 0.12345678912345678
diff --git a/upb/lex/BUILD b/upb/lex/BUILD
index b12e37d041..efcf9e9e40 100644
--- a/upb/lex/BUILD
+++ b/upb/lex/BUILD
@@ -41,6 +41,16 @@ cc_test(
     ],
 )
 
+cc_test(
+    name = "round_trip_test",
+    srcs = ["round_trip_test.cc"],
+    deps = [
+        ":lex",
+        "@com_google_googletest//:gtest",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
 # begin:github_only
 filegroup(
     name = "source_files",
diff --git a/upb/lex/round_trip.c b/upb/lex/round_trip.c
index 13104341b1..82818eea23 100644
--- a/upb/lex/round_trip.c
+++ b/upb/lex/round_trip.c
@@ -8,6 +8,8 @@
 #include "upb/lex/round_trip.h"
 
 #include <float.h>
+#include <math.h>
+#include <stdio.h>
 #include <stdlib.h>
 
 // Must be last.
@@ -28,6 +30,10 @@ static void upb_FixLocale(char* p) {
 
 void _upb_EncodeRoundTripDouble(double val, char* buf, size_t size) {
   assert(size >= kUpb_RoundTripBufferSize);
+  if (isnan(val)) {
+    snprintf(buf, size, "%s", "nan");
+    return;
+  }
   snprintf(buf, size, "%.*g", DBL_DIG, val);
   if (strtod(buf, NULL) != val) {
     snprintf(buf, size, "%.*g", DBL_DIG + 2, val);
@@ -38,6 +44,10 @@ void _upb_EncodeRoundTripDouble(double val, char* buf, size_t size) {
 
 void _upb_EncodeRoundTripFloat(float val, char* buf, size_t size) {
   assert(size >= kUpb_RoundTripBufferSize);
+  if (isnan(val)) {
+    snprintf(buf, size, "%s", "nan");
+    return;
+  }
   snprintf(buf, size, "%.*g", FLT_DIG, val);
   if (strtof(buf, NULL) != val) {
     snprintf(buf, size, "%.*g", FLT_DIG + 3, val);
diff --git a/upb/lex/round_trip_test.cc b/upb/lex/round_trip_test.cc
new file mode 100644
index 0000000000..c6fc718522
--- /dev/null
+++ b/upb/lex/round_trip_test.cc
@@ -0,0 +1,35 @@
+#include "upb/lex/round_trip.h"
+
+#include <math.h>
+
+#include <gtest/gtest.h>
+
+namespace {
+
+TEST(RoundTripTest, Double) {
+  char buf[32];
+
+  _upb_EncodeRoundTripDouble(0.123456789, buf, sizeof(buf));
+  EXPECT_STREQ(buf, "0.123456789");
+
+  _upb_EncodeRoundTripDouble(0.0, buf, sizeof(buf));
+  EXPECT_STREQ(buf, "0");
+
+  _upb_EncodeRoundTripDouble(nan(""), buf, sizeof(buf));
+  EXPECT_STREQ(buf, "nan");
+}
+
+TEST(RoundTripTest, Float) {
+  char buf[32];
+
+  _upb_EncodeRoundTripFloat(0.123456, buf, sizeof(buf));
+  EXPECT_STREQ(buf, "0.123456");
+
+  _upb_EncodeRoundTripFloat(0.0, buf, sizeof(buf));
+  EXPECT_STREQ(buf, "0");
+
+  _upb_EncodeRoundTripFloat(nan(""), buf, sizeof(buf));
+  EXPECT_STREQ(buf, "nan");
+}
+
+}  // namespace