diff --git a/BUILD b/BUILD
index 3cac4a865..c4de1c4c9 100644
--- a/BUILD
+++ b/BUILD
@@ -462,11 +462,11 @@ genrule(
     name = "gen_well_known_protos_java",
     srcs = WELL_KNOWN_PROTOS,
     outs = [
-        "wellknown.srcjar"
+        "wellknown.srcjar",
     ],
     cmd = "$(location :protoc) --java_out=$(@D)/wellknown.jar" +
-        " -Isrc $(SRCS) " +
-        " && mv $(@D)/wellknown.jar $(@D)/wellknown.srcjar",
+          " -Isrc $(SRCS) " +
+          " && mv $(@D)/wellknown.jar $(@D)/wellknown.srcjar",
     tools = [":protoc"],
 )
 
@@ -539,7 +539,10 @@ cc_binary(
     ]),
     copts = COPTS + [
         "-DGOOGLE_PROTOBUF_HAS_ONEOF=1",
-    ],
+    ] + select({
+        "//conditions:default": [],
+        ":allow_oversize_protos": ["-DPROTOBUF_PYTHON_ALLOW_OVERSIZE_PROTOS=1"],
+    }),
     includes = [
         "python/",
         "src/",
@@ -561,6 +564,13 @@ config_setting(
     },
 )
 
+config_setting(
+    name = "allow_oversize_protos",
+    values = {
+        "define": "allow_oversize_protos=true",
+    },
+)
+
 py_proto_library(
     name = "protobuf_python",
     srcs = WELL_KNOWN_PROTOS,
diff --git a/python/google/protobuf/pyext/message.cc b/python/google/protobuf/pyext/message.cc
index 863cde013..60ec9c1b9 100644
--- a/python/google/protobuf/pyext/message.cc
+++ b/python/google/protobuf/pyext/message.cc
@@ -1921,6 +1921,15 @@ static PyObject* MergeFromString(CMessage* self, PyObject* arg) {
   AssureWritable(self);
   io::CodedInputStream input(
       reinterpret_cast<const uint8*>(data), data_length);
+#if PROTOBUF_PYTHON_ALLOW_OVERSIZE_PROTOS
+  // Protobuf has a 64MB limit built in, this code will override this. Please do
+  // not enable this unless you fully understand the implications: protobufs
+  // must all be kept in memory at the same time, so if they grow too big you
+  // may get OOM errors. The protobuf APIs do not provide any tools for
+  // processing protobufs in chunks.  If you have protos this big you should
+  // break them up if it is at all convenient to do so.
+  input.SetTotalBytesLimit(INT_MAX, INT_MAX);
+#endif  // PROTOBUF_PYTHON_ALLOW_OVERSIZE_PROTOS
   PyDescriptorPool* pool = GetDescriptorPoolForMessage(self);
   input.SetExtensionRegistry(pool->pool, pool->message_factory);
   bool success = self->message->MergePartialFromCodedStream(&input);