diff --git a/sys/boot/i386/boot2/boot2.c b/sys/boot/i386/boot2/boot2.c
index 7850bc178437..4f6229674c0c 100644
--- a/sys/boot/i386/boot2/boot2.c
+++ b/sys/boot/i386/boot2/boot2.c
@@ -133,7 +133,7 @@ static inline int
 strcmp(const char *s1, const char *s2)
 {
     for (; *s1 == *s2 && *s1; s1++, s2++);
-    return *s1 - *s2;
+    return (unsigned char)*s1 - (unsigned char)*s2;
 }
 
 #include "ufsread.c"
diff --git a/sys/boot/i386/gptboot/gptboot.c b/sys/boot/i386/gptboot/gptboot.c
index 7850bc178437..4f6229674c0c 100644
--- a/sys/boot/i386/gptboot/gptboot.c
+++ b/sys/boot/i386/gptboot/gptboot.c
@@ -133,7 +133,7 @@ static inline int
 strcmp(const char *s1, const char *s2)
 {
     for (; *s1 == *s2 && *s1; s1++, s2++);
-    return *s1 - *s2;
+    return (unsigned char)*s1 - (unsigned char)*s2;
 }
 
 #include "ufsread.c"