diff --git a/indra/llcommon/llerror.h b/indra/llcommon/llerror.h
index f841637b3..60f3bfad1 100644
--- a/indra/llcommon/llerror.h
+++ b/indra/llcommon/llerror.h
@@ -303,7 +303,7 @@ typedef LLError::NoClassInfo _LL_CLASS_TO_LOG;
 	*/
 
 #ifdef SHOW_ASSERT
-extern bool is_main_thread();
+extern LL_COMMON_API bool is_main_thread();
 #endif
 
 #endif // LL_LLERROR_H
diff --git a/indra/llcommon/llthread.h b/indra/llcommon/llthread.h
index 2146216aa..fa003afdd 100644
--- a/indra/llcommon/llthread.h
+++ b/indra/llcommon/llthread.h
@@ -41,7 +41,7 @@
 #include "aiaprpool.h"
 
 #ifdef SHOW_ASSERT
-extern bool is_main_thread(void);
+extern LL_COMMON_API bool is_main_thread(void);
 #endif
 
 class LLThread;