1 files changed, 4 insertions, 4 deletions

diff --git a/source/tools/acpidump/apfiles.c b/source/tools/acpidump/apfiles.c
index 9c187271371b..1b05984da567 100644
--- a/source/tools/acpidump/apfiles.c
+++ b/source/tools/acpidump/apfiles.c
@@ -159,10 +159,10 @@ ApWriteToBinaryFile (
     {
         ACPI_MOVE_NAME (Filename, Table->Signature);
     }
-    Filename[0] = (char) tolower (Filename[0]);
-    Filename[1] = (char) tolower (Filename[1]);
-    Filename[2] = (char) tolower (Filename[2]);
-    Filename[3] = (char) tolower (Filename[3]);
+    Filename[0] = (char) tolower ((int) Filename[0]);
+    Filename[1] = (char) tolower ((int) Filename[1]);
+    Filename[2] = (char) tolower ((int) Filename[2]);
+    Filename[3] = (char) tolower ((int) Filename[3]);
     Filename[ACPI_NAME_SIZE] = 0;
 
     /* Handle multiple SSDTs - create different filenames for each */