diff --git a/tools/exetool.c b/tools/exetool.c
index 571d994..d034cab 100644
--- a/tools/exetool.c
+++ b/tools/exetool.c
@@ -167,7 +167,7 @@ int main(int argc, char *argv[])
     fread(&SubSystem, sizeof(unsigned short), 1, ExeFile);
 
     /* Seek back to the SubSystem field in the optional header */
-    fseek(ExeFile, -sizeof(unsigned short), SEEK_CUR);
+    fseek(ExeFile, -(long)sizeof(unsigned short), SEEK_CUR);
 
     /* Write the new SubSystem value */
     fwrite(&NewSubSystem->Identifier, sizeof(unsigned short), 1, ExeFile);