diff --git a/pkgs/os-specific/linux/syslinux/default.nix b/pkgs/os-specific/linux/syslinux/default.nix
index 93e5d591a9d9..3c01516b0815 100644
--- a/pkgs/os-specific/linux/syslinux/default.nix
+++ b/pkgs/os-specific/linux/syslinux/default.nix
@@ -8,7 +8,8 @@ stdenv.mkDerivation rec {
     sha256 = "03l5iifwlg1wyb4yh98i0b7pd4j55a1c9y74q1frs47a5dnrilr6";
   };
 
-  patches = [ ./perl-deps.patch ];
+  # gcc5-fix should be in 6.04+, so remove if it fails to apply.
+  patches = [ ./perl-deps.patch ./gcc5-fix.patch ];
 
   buildInputs = [ nasm perl libuuid ];
 
diff --git a/pkgs/os-specific/linux/syslinux/gcc5-fix.patch b/pkgs/os-specific/linux/syslinux/gcc5-fix.patch
new file mode 100644
index 000000000000..dc44b1880583
--- /dev/null
+++ b/pkgs/os-specific/linux/syslinux/gcc5-fix.patch
@@ -0,0 +1,26 @@
+diff --git a/com32/include/menu.h b/com32/include/menu.h
+index bc0182f..b0251e4 100644
+--- a/com32/include/menu.h
++++ b/com32/include/menu.h
+@@ -195,7 +195,7 @@ void local_cursor_enable(bool);
+ 
+ static inline int my_isspace(char c)
+ {
+-    return (unsigned char)c <= ' ';
++    return (unsigned char)c <= ' ' || (unsigned char)c == '\x7f';
+ }
+ 
+ int my_isxdigit(char c);
+diff --git a/com32/menu/readconfig.c b/com32/menu/readconfig.c
+index b7814be..a433fad 100644
+--- a/com32/menu/readconfig.c
++++ b/com32/menu/readconfig.c
+@@ -299,7 +299,7 @@ static char *copy_sysappend_string(char *dst, const char *src)
+     char c;
+ 
+     while ((c = *src++)) {
+-	if (c <= ' ' && c == '\x7f') {
++	if (my_isspace(c)) {
+ 	    if (!was_space)
+ 		*dst++ = '_';
+ 	    was_space = true;