diff --git a/src/vmp_stack.c b/src/vmp_stack.c
index ed12e8ad..d1dcb2c7 100644
--- a/src/vmp_stack.c
+++ b/src/vmp_stack.c
@@ -229,7 +229,7 @@ int vmp_walk_and_record_stack(PY_STACK_FRAME_T *frame, void ** result,
         while (signal < 0) {
             int err = unw_step(&cursor);
             if (err <= 0) {
-                fprintf("WARNING: did not find signal frame, skipping sample\n");
+                fprintf(stderr, "WARNING: did not find signal frame, skipping sample\n");
                 return 0;
             }
             signal++;
@@ -244,7 +244,7 @@ int vmp_walk_and_record_stack(PY_STACK_FRAME_T *frame, void ** result,
             }
             int err = unw_step(&cursor);
             if (err <= 0) {
-                fprintf("WARNING: did not find signal frame, skipping sample\n");
+                fprintf(stderr,"WARNING: did not find signal frame, skipping sample\n");
                 return 0;
             }
         }
diff --git a/src/vmprof_main.h b/src/vmprof_main.h
index 1acda2cb..a85ae8d0 100644
--- a/src/vmprof_main.h
+++ b/src/vmprof_main.h
@@ -232,7 +232,7 @@ static void sigprof_handler(int sig_nr, siginfo_t* info, void *ucontext)
             if (commit) {
                 commit_buffer(fd, p);
             } else {
-                fprintf("WARNING: canceled buffer, no stack trace was written\n");
+                fprintf(stderr, "WARNING: canceled buffer, no stack trace was written\n");
                 cancel_buffer(p);
             }
         }