diff --git a/include/haproxy/base64.h b/include/haproxy/base64.h
index d7dec58cd..1756bc058 100644
--- a/include/haproxy/base64.h
+++ b/include/haproxy/base64.h
@@ -14,7 +14,7 @@
 #ifndef _HAPROXY_BASE64_H
 #define _HAPROXY_BASE64_H
 
-#include <stddef.h>
+#include <haproxy/api.h>
 
 int a2base64(char *in, int ilen, char *out, int olen);
 int base64dec(const char *in, size_t ilen, char *out, size_t olen);
diff --git a/include/haproxy/buf-t.h b/include/haproxy/buf-t.h
index cb4310da0..3c0f8b551 100644
--- a/include/haproxy/buf-t.h
+++ b/include/haproxy/buf-t.h
@@ -28,7 +28,7 @@
 #ifndef _HAPROXY_BUF_T_H
 #define _HAPROXY_BUF_T_H
 
-#include <stddef.h>
+#include <haproxy/api-t.h>
 
 /* Structure defining a buffer's head */
 struct buffer {
diff --git a/include/haproxy/http.h b/include/haproxy/http.h
index 64ac4bcec..1bd9da9ad 100644
--- a/include/haproxy/http.h
+++ b/include/haproxy/http.h
@@ -23,9 +23,9 @@
 #ifndef _HAPROXY_HTTP_H
 #define _HAPROXY_HTTP_H
 
-#include <stddef.h>
 #include <string.h>
 #include <import/ist.h>
+#include <haproxy/api.h>
 #include <haproxy/http-t.h>
 
 extern const int http_err_codes[HTTP_ERR_SIZE];
diff --git a/include/haproxy/namespace-t.h b/include/haproxy/namespace-t.h
index 3a9733644..b86ae31a5 100644
--- a/include/haproxy/namespace-t.h
+++ b/include/haproxy/namespace-t.h
@@ -23,8 +23,8 @@
 #ifndef _HAPROXY_NAMESPACE_T_H
 #define _HAPROXY_NAMESPACE_T_H
 
-#include <stddef.h>
 #include <import/ebpttree.h>
+#include <haproxy/api-t.h>
 
 /* the struct is just empty if namespaces are not supported */
 struct netns_entry