kc3-lang/smtp

diff --git a/src/smtp.c b/src/smtp.c
index 5734258..f90b090 100644
--- a/src/smtp.c
+++ b/src/smtp.c
@@ -53,13 +53,6 @@
 # include <openssl/x509v3.h>
 #endif /* SMTP_OPENSSL */
 
-#ifndef SIZE_MAX
-/**
- * Maximum value of size_t type.
- */
-# define SIZE_MAX ((size_t)(-1))
-#endif /* SIZE_MAX */
-
 /**
  * Get access to the @ref smtp_result_code and @ref smtp_command definitions.
  */
diff --git a/src/smtp.h b/src/smtp.h
index e52e2f1..f035cc5 100644
--- a/src/smtp.h
+++ b/src/smtp.h
@@ -16,6 +16,13 @@
 #include <stddef.h>
 #include <stdio.h>
 
+#ifndef SIZE_MAX
+/**
+ * Maximum value of size_t type.
+ */
+# define SIZE_MAX ((size_t)(-1))
+#endif /* SIZE_MAX */
+
 /**
  * Status codes indicating success or failure from calling any of the
  * SMTP library functions.