diff --git a/lib/gears/shape.lua b/lib/gears/shape.lua
index b89563c6..6c6bf223 100644
--- a/lib/gears/shape.lua
+++ b/lib/gears/shape.lua
@@ -472,8 +472,11 @@ function module.arc(cr, width, height, thickness, start_angle, end_angle, start_
     if end_rounded then
         arc_length = arc_length - thickness/2
 
-        -- And back to angles
-        end_angle = start_angle + (arc_length/(radius - thickness/2))
+        -- And back to angles. Also make sure to avoid underflowing when the
+        -- rounded edge radius is greater than the angle delta.
+        end_angle = start_angle + math.max(
+            0, arc_length/(radius - thickness/2)
+        )
     end
 
     -- The path is a curcular arc joining 4 points
diff --git a/lib/wibox/container/arcchart.lua b/lib/wibox/container/arcchart.lua
index 8efe4df2..f2754146 100644
--- a/lib/wibox/container/arcchart.lua
+++ b/lib/wibox/container/arcchart.lua
@@ -104,10 +104,11 @@ function arcchart:after_draw_children(_, cr, width, height)
     local max_val = self:get_max_value()
     local sum = 0
 
+    for _, v in ipairs(values) do
+        sum = sum + v
+    end
+
     if not max_val then
-        for _, v in ipairs(values) do
-            sum = sum + v
-        end
         max_val = sum
     end
 
@@ -131,7 +132,7 @@ function arcchart:after_draw_children(_, cr, width, height)
 
         shape.arc(cr, wa.width-border_width, wa.height-border_width,
             thickness+border_width, math.pi-end_angle, math.pi-start_angle,
-            (use_rounded_edges and k == 1), (use_rounded_edges and k == #values)
+            (use_rounded_edges and k == #values), (use_rounded_edges and k == 1)
         )
 
         cr:fill()