diff --git a/I7000/i701_sys.c b/I7000/i701_sys.c
index 3d4acc0f..28dceb21 100644
--- a/I7000/i701_sys.c
+++ b/I7000/i701_sys.c
@@ -446,7 +446,7 @@ parse_sym(CONST char *cptr, t_addr addr, UNIT * uptr, t_value * val, int32 sw)
         i = 0;
         while (*cptr != '\0' && i < 6) {
             d <<= 6;
-            if (sim_ascii_to_six[0177 & *cptr] != -1)
+            if (sim_ascii_to_six[0177 & *cptr] != (const char)-1)
                 d |= sim_ascii_to_six[0177 & *cptr];
             cptr++;
             i++;
diff --git a/I7000/i7070_sys.c b/I7000/i7070_sys.c
index 1908dfa1..d485af3c 100644
--- a/I7000/i7070_sys.c
+++ b/I7000/i7070_sys.c
@@ -1068,7 +1068,7 @@ parse_sym(CONST char *cptr, t_addr addr, UNIT * uptr, t_value * val, int32 sw)
         i = 0;
         while (*cptr != '\0' && i < 5) {
             d <<= 8;
-            if (sim_ascii_to_six[0177 & *cptr] != -1)
+            if (sim_ascii_to_six[0177 & *cptr] != (const char)-1)
                 d |= bcd_mem[(int)sim_ascii_to_six[0177 & *cptr]];
             cptr++;
             i++;
diff --git a/I7000/i7090_sys.c b/I7000/i7090_sys.c
index f3e30fd9..41a2b07c 100644
--- a/I7000/i7090_sys.c
+++ b/I7000/i7090_sys.c
@@ -1025,7 +1025,7 @@ parse_sym(CONST char *cptr, t_addr addr, UNIT * uptr, t_value * val, int32 sw)
         i = 0;
         while (*cptr != '\0' && i < 6) {
             d <<= 6;
-            if (ascii_to_mem[0177 & *cptr] != -1)
+            if (ascii_to_mem[0177 & *cptr] != (const char)-1)
                 d |= ascii_to_mem[0177 & *cptr];
             cptr++;
             i++;