diff --git a/proc.h b/proc.h
index f530e5d..0dfa7db 100644
--- a/proc.h
+++ b/proc.h
@@ -107,7 +107,7 @@
 	unsigned int personality;
 	int tracesysgood;         /* signal indicating a PTRACE_SYSCALL trap */
 
-	int callstack_depth;
+	size_t callstack_depth;
 	struct callstack_element callstack[MAX_CALLDEPTH];
 
 	/* Linked list of libraries in backwards order of mapping.