--- a/liboctave/util/oct-inttypes.h
+++ b/liboctave/util/oct-inttypes.h
@@ -830,6 +830,11 @@
 
   octave_int (T i) : ival (i) { }
 
+  // Always treat characters as unsigned.
+  octave_int (char c)
+    : ival (octave_int_base<T>::truncate_int (static_cast<unsigned char> (c)))
+  { }
+
   octave_int (double d) : ival (octave_int_base<T>::convert_real (d)) { }
 
   octave_int (float d) : ival (octave_int_base<T>::convert_real (d)) { }

--- a/scripts/plot/draw/fplot.m
+++ b/scripts/plot/draw/fplot.m
@@ -146,10 +146,10 @@
   ##        problems with the current solution.
 
   while (n < 2^18)    # Something is wrong if we need more than 250K points
-    yi = interp1 (x0, y0, x, "linear");
+    yi = interp1 (x0, y0, x, "linear")
     ## relative error calculation using average of [yi,y] as reference
     ## since neither estimate is known a priori to be better than the other.
-    err = 0.5 * max (abs ((yi - y) ./ (yi + y))(:));
+    err = 0.5 * max (abs ((yi - y) ./ (yi + y))(:))
     if (err < tol || abs (err - err0) < tol/2)
       ## Either relative tolerance has been met OR
       ## algorithm has stopped making any reasonable progress per iteration.