diff --git a/win32/sendmail.c b/win32/sendmail.c
index 80dff3f3907..fbb2ae02989 100644
--- a/win32/sendmail.c
+++ b/win32/sendmail.c
@@ -63,7 +63,7 @@ char seps[] = " ,\t\n";
 char *php_mailer = "PHP 7 WIN32";
 
 /* Error messages */
-static char *ErrorMessages[] =
+static const char *ErrorMessages[] =
 {
 	"Success", /* 0 */
 	"Bad arguments from form", /* 1 */
@@ -328,7 +328,7 @@ PHPAPI void TSMClose(void)
 // Author/Date:  jcar 20/9/96
 // History:
 //*********************************************************************
-PHPAPI char *GetSMErrorText(int index)
+PHPAPI const char *GetSMErrorText(int index)
 {
 	if (MIN_ERROR_INDEX <= index && index < MAX_ERROR_INDEX) {
 		return (ErrorMessages[index]);
diff --git a/win32/sendmail.h b/win32/sendmail.h
index e6096f789eb..6cfdc5706f1 100644
--- a/win32/sendmail.h
+++ b/win32/sendmail.h
@@ -36,5 +36,5 @@ PHPAPI int TSendMail(const char *host, int *error, char **error_message,
 			  const char *headers, const char *Subject, const char *mailTo, const char *data,
 			  char *mailCc, char *mailBcc, char *mailRPath);
 PHPAPI void TSMClose(void);
-PHPAPI char *GetSMErrorText(int index);
+PHPAPI const char *GetSMErrorText(int index);
 #endif							/* sendmail_h */