diff --git a/ext/standard/formatted_print.c b/ext/standard/formatted_print.c
index a21bfebe42b..a10e90bf0ab 100644
--- a/ext/standard/formatted_print.c
+++ b/ext/standard/formatted_print.c
@@ -28,6 +28,7 @@
 #ifdef HAVE_LOCALE_H
 #include <locale.h>
 #ifdef ZTS
+#include "ext/standard/php_string.h"
 #define LCONV_DECIMAL_POINT (*lconv.decimal_point)
 #else
 #define LCONV_DECIMAL_POINT (*lconv->decimal_point)
diff --git a/main/snprintf.c b/main/snprintf.c
index 64b66336553..d3382d33831 100644
--- a/main/snprintf.c
+++ b/main/snprintf.c
@@ -39,6 +39,7 @@
 #ifdef HAVE_LOCALE_H
 #include <locale.h>
 #ifdef ZTS
+#include "ext/standard/php_string.h"
 #define LCONV_DECIMAL_POINT (*lconv.decimal_point)
 #else
 #define LCONV_DECIMAL_POINT (*lconv->decimal_point)
diff --git a/main/spprintf.c b/main/spprintf.c
index 212914fe9d5..ff8e9643dee 100644
--- a/main/spprintf.c
+++ b/main/spprintf.c
@@ -94,6 +94,7 @@
 #ifdef HAVE_LOCALE_H
 #include <locale.h>
 #ifdef ZTS
+#include "ext/standard/php_string.h"
 #define LCONV_DECIMAL_POINT (*lconv.decimal_point)
 #else
 #define LCONV_DECIMAL_POINT (*lconv->decimal_point)