diff --git a/vlib/builtin/cdefs.v b/vlib/builtin/cdefs.v
index ba280e73bc..48cb0f95f3 100644
--- a/vlib/builtin/cdefs.v
+++ b/vlib/builtin/cdefs.v
@@ -1,6 +1,6 @@
 module builtin
 
-fn backtrace(a voidptr, b int) int
+fn C.backtrace(a voidptr, b int) int
 
 fn C.memcpy(byteptr, byteptr, int)
 fn C.memmove(byteptr, byteptr, int)
@@ -14,7 +14,7 @@ fn C.strlen(s byteptr) int
 
 
 
-fn backtrace_symbols_fd(voidptr, int, int)
+fn C.backtrace_symbols_fd(voidptr, int, int)
 
 
 
diff --git a/vlib/compiler/cheaders.v b/vlib/compiler/cheaders.v
index 47404d44ef..86406bf3f0 100644
--- a/vlib/compiler/cheaders.v
+++ b/vlib/compiler/cheaders.v
@@ -21,12 +21,12 @@ CommonCHeaders = '
 
 #ifdef __APPLE__
 #include <libproc.h> // proc_pidpath
-//#include <execinfo.h> // backtrace and backtrace_symbols_fd
+#include <execinfo.h> // backtrace and backtrace_symbols_fd
 #endif
 
 #ifdef __linux__
 //#if !defined(__BIONIC__) && !defined(__GNUC_PREREQ)
-//#include <execinfo.h> // backtrace and backtrace_symbols_fd
+#include <execinfo.h> // backtrace and backtrace_symbols_fd
 //#endif
 
 #pragma weak backtrace