diff --git a/src/Util/Asserts.h b/src/Util/Asserts.h
index 6b94d56ac..d0cfbc728 100755
--- a/src/Util/Asserts.h
+++ b/src/Util/Asserts.h
@@ -1,7 +1,5 @@
 //
-//  Asserts.h
-//
-//  Copyright (c) 2016 Open Whisper Systems. All rights reserved.
+//  Copyright (c) 2017 Open Whisper Systems. All rights reserved.
 //
 
 #import <Foundation/Foundation.h>
@@ -21,9 +19,18 @@ NSLog(@"Assertion failed: %s", CONVERT_EXPR_TO_STRING(X)); \
 NSAssert(0, @"Assertion failed: %s", CONVERT_EXPR_TO_STRING(X)); \
 }
 
+// OWSAssert() should be used in Obj-C and Swift methods.
+// OWSCAssert() should be used in free functions.
+#define OWSCAssert(X) \
+if (!(X)) { \
+NSLog(@"Assertion failed: %s", CONVERT_EXPR_TO_STRING(X)); \
+NSCAssert(0, @"Assertion failed: %s", CONVERT_EXPR_TO_STRING(X)); \
+}
+
 #else
 
 #define OWSAssert(X)
+#define OWSCAssert(X)
 
 #endif
 
diff --git a/src/Util/OWSDispatch.h b/src/Util/OWSDispatch.h
index 8d6b42985..7da5da39f 100644
--- a/src/Util/OWSDispatch.h
+++ b/src/Util/OWSDispatch.h
@@ -24,4 +24,6 @@ NS_ASSUME_NONNULL_BEGIN
 
 @end
 
+void AssertIsOnMainThread();
+
 NS_ASSUME_NONNULL_END
diff --git a/src/Util/OWSDispatch.m b/src/Util/OWSDispatch.m
index 6d3353100..89a4aef96 100644
--- a/src/Util/OWSDispatch.m
+++ b/src/Util/OWSDispatch.m
@@ -40,4 +40,8 @@ NS_ASSUME_NONNULL_BEGIN
 
 @end
 
+void AssertIsOnMainThread() {
+    OWSCAssert([NSThread isMainThread]);
+}
+
 NS_ASSUME_NONNULL_END