diff --git a/objectivec/GPBMessage.m b/objectivec/GPBMessage.m
index 94d179b..3da85b5 100644
--- a/objectivec/GPBMessage.m
+++ b/objectivec/GPBMessage.m
@@ -556,6 +556,7 @@
   id array = GPBGetObjectIvarWithFieldNoAutocreate(self, field);
   if (!array) {
     // Check again after getting the lock.
+    GPBPrepareReadOnlySemaphore(self);
     dispatch_semaphore_wait(self->readOnlySemaphore_, DISPATCH_TIME_FOREVER);
     array = GPBGetObjectIvarWithFieldNoAutocreate(self, field);
     if (!array) {
@@ -586,6 +587,7 @@
   id dict = GPBGetObjectIvarWithFieldNoAutocreate(self, field);
   if (!dict) {
     // Check again after getting the lock.
+    GPBPrepareReadOnlySemaphore(self);
     dispatch_semaphore_wait(self->readOnlySemaphore_, DISPATCH_TIME_FOREVER);
     dict = GPBGetObjectIvarWithFieldNoAutocreate(self, field);
     if (!dict) {
@@ -791,8 +793,6 @@
   if ((self = [super init])) {
     messageStorage_ = (GPBMessage_StoragePtr)(
         ((uint8_t *)self) + class_getInstanceSize([self class]));
-
-    readOnlySemaphore_ = dispatch_semaphore_create(1);
   }
 
   return self;
@@ -868,7 +868,9 @@
 - (void)dealloc {
   [self internalClear:NO];
   NSCAssert(!autocreator_, @"Autocreator was not cleared before dealloc.");
-  dispatch_release(readOnlySemaphore_);
+  if (readOnlySemaphore_) {
+    dispatch_release(readOnlySemaphore_);
+  }
   [super dealloc];
 }
 
@@ -1706,6 +1708,7 @@
   }
 
   // Check for an autocreated value.
+  GPBPrepareReadOnlySemaphore(self);
   dispatch_semaphore_wait(readOnlySemaphore_, DISPATCH_TIME_FOREVER);
   value = [autocreatedExtensionMap_ objectForKey:extension];
   if (!value) {
diff --git a/objectivec/GPBMessage_PackagePrivate.h b/objectivec/GPBMessage_PackagePrivate.h
index b7e24fc..478db2c 100644
--- a/objectivec/GPBMessage_PackagePrivate.h
+++ b/objectivec/GPBMessage_PackagePrivate.h
@@ -67,6 +67,10 @@
   // priority inversion:
   //   http://mjtsai.com/blog/2015/12/16/osspinlock-is-unsafe/
   //   https://lists.swift.org/pipermail/swift-dev/Week-of-Mon-20151214/000372.html
+  // Use of readOnlySemaphore_ must be prefaced by a call to
+  // GPBPrepareReadOnlySemaphore to ensure it has been created. This allows
+  // readOnlySemaphore_ to be only created when actually needed.
+  dispatch_once_t readOnlySemaphoreCreationOnce_;
   dispatch_semaphore_t readOnlySemaphore_;
 }
 
@@ -103,6 +107,14 @@
 
 CF_EXTERN_C_BEGIN
 
+
+// Call this before using the readOnlySemaphore_. This ensures it is created only once.
+NS_INLINE void GPBPrepareReadOnlySemaphore(GPBMessage *self) {
+  dispatch_once(&self->readOnlySemaphoreCreationOnce_, ^{
+    self->readOnlySemaphore_ = dispatch_semaphore_create(1);
+  });
+}
+
 // Returns a new instance that was automatically created by |autocreator| for
 // its field |field|.
 GPBMessage *GPBCreateMessageWithAutocreator(Class msgClass,
diff --git a/objectivec/GPBUtilities.m b/objectivec/GPBUtilities.m
index 3e9d11c..447c749 100644
--- a/objectivec/GPBUtilities.m
+++ b/objectivec/GPBUtilities.m
@@ -412,6 +412,7 @@
     return field.defaultValue.valueMessage;
   }
 
+  GPBPrepareReadOnlySemaphore(self);
   dispatch_semaphore_wait(self->readOnlySemaphore_, DISPATCH_TIME_FOREVER);
   GPBMessage *result = GPBGetObjectIvarWithFieldNoAutocreate(self, field);
   if (!result) {