diff --git a/AK/kstdio.h b/AK/kstdio.h
index 05b06365d8..7557af14b2 100644
--- a/AK/kstdio.h
+++ b/AK/kstdio.h
@@ -45,6 +45,6 @@ inline int dbgputstr(const char (&array)[N])
 #else
 #    include <stdio.h>
 #    define kprintf printf
-#    define dbgprintf printf
-#    define dbgputstr(characters, length) fwrite(characters, 1, length, stdout)
+#    define dbgprintf(...) fprintf(stderr, __VA_ARGS__)
+#    define dbgputstr(characters, length) fwrite(characters, 1, length, stderr)
 #endif
diff --git a/Libraries/LibCore/IODevice.cpp b/Libraries/LibCore/IODevice.cpp
index a727f522b2..3ee2ea0317 100644
--- a/Libraries/LibCore/IODevice.cpp
+++ b/Libraries/LibCore/IODevice.cpp
@@ -182,7 +182,7 @@ ByteBuffer IODevice::read_line(size_t max_size)
         return {};
     if (m_eof) {
         if (m_buffered_data.size() > max_size) {
-            dbgprintf("IODevice::read_line: At EOF but there's more than max_size(%d) buffered\n", max_size);
+            dbgprintf("IODevice::read_line: At EOF but there's more than max_size(%zu) buffered\n", max_size);
             return {};
         }
         auto buffer = ByteBuffer::copy(m_buffered_data.data(), m_buffered_data.size());