diff --git a/ChangeLog.md b/ChangeLog.md
index 82529b9..290056d 100644
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -3,6 +3,7 @@
 ### Internal
 
 - Add builds with gcc-9 to CI.
+- Fix invalid pointer to integer cast that might cause problems on some platforms.
 
 ## v0.4.1
 
diff --git a/lib/fort.c b/lib/fort.c
index 47bc0d5..6c5e3d6 100644
--- a/lib/fort.c
+++ b/lib/fort.c
@@ -6867,7 +6867,7 @@ int buffer_check_align(f_string_buffer_t *buffer)
             return 1;
 #ifdef FT_HAVE_WCHAR
         case W_CHAR_BUF:
-            return (((unsigned long)buffer->str.data) & (sizeof(wchar_t) - 1)) == 0;
+            return (((uintptr_t)buffer->str.data) & (sizeof(wchar_t) - 1)) == 0;
 #endif
 #ifdef FT_HAVE_UTF8
         case UTF8_BUF:
diff --git a/src/string_buffer.c b/src/string_buffer.c
index dfafbcc..cb2f6f1 100644
--- a/src/string_buffer.c
+++ b/src/string_buffer.c
@@ -685,7 +685,7 @@ int buffer_check_align(f_string_buffer_t *buffer)
             return 1;
 #ifdef FT_HAVE_WCHAR
         case W_CHAR_BUF:
-            return (((unsigned long)buffer->str.data) & (sizeof(wchar_t) - 1)) == 0;
+            return (((uintptr_t)buffer->str.data) & (sizeof(wchar_t) - 1)) == 0;
 #endif
 #ifdef FT_HAVE_UTF8
         case UTF8_BUF: