diff --git a/bolt/test/Inputs/asm_main.c b/bolt/test/Inputs/asm_main.c
index fa5f5c379848..f67f6c481a42 100644
--- a/bolt/test/Inputs/asm_main.c
+++ b/bolt/test/Inputs/asm_main.c
@@ -1,3 +1,5 @@
+void foo(void);
+
 int main() {
   foo();
   return 0;
diff --git a/cross-project-tests/debuginfo-tests/dexter-tests/dbg-arg.c b/cross-project-tests/debuginfo-tests/dexter-tests/dbg-arg.c
index 0ef27a09598e..e4f4c3448e78 100644
--- a/cross-project-tests/debuginfo-tests/dexter-tests/dbg-arg.c
+++ b/cross-project-tests/debuginfo-tests/dexter-tests/dbg-arg.c
@@ -18,6 +18,7 @@ struct _mtx
   } mtxi;
 };
 
+int bar(int, int);
 
 int foobar(struct _mtx *mutex) {
   int r = 1;
diff --git a/lldb/test/API/functionalities/thread/exit_during_expression/main.c b/lldb/test/API/functionalities/thread/exit_during_expression/main.c
index a3bf53915a03..eb6d17520986 100644
--- a/lldb/test/API/functionalities/thread/exit_during_expression/main.c
+++ b/lldb/test/API/functionalities/thread/exit_during_expression/main.c
@@ -5,6 +5,8 @@
 
 static unsigned int g_timeout = 100000;
 
+extern int usleep(unsigned int);
+
 int function_to_call() {
 
   errno = 0;