diff --git a/src/terminal/Screen.zig b/src/terminal/Screen.zig
index 5376864d2..1ecc1656e 100644
--- a/src/terminal/Screen.zig
+++ b/src/terminal/Screen.zig
@@ -566,7 +566,7 @@ fn scrollDelta(self: *Screen, delta: isize, grow: bool) !void {
     if (!grow) {
         self.viewport = @minimum(
             self.history,
-            self.viewport +| @intCast(usize, delta),
+            self.viewport + @intCast(usize, delta),
         );
         return;
     }
@@ -574,7 +574,7 @@ fn scrollDelta(self: *Screen, delta: isize, grow: bool) !void {
     // Add our delta to our viewport. If we're less than the max currently
     // allowed to scroll to the bottom (the end of the history), then we
     // have space and we just return.
-    self.viewport +|= @intCast(usize, delta);
+    self.viewport += @intCast(usize, delta);
     if (self.viewport <= self.history) return;
 
     // Our viewport is bigger than our max. The number of new rows we need
@@ -610,10 +610,6 @@ fn scrollDelta(self: *Screen, delta: isize, grow: bool) !void {
         const rows_to_delete = rows_final - self.rowsCapacity();
         self.viewport -= rows_to_delete;
         self.storage.deleteOldest(rows_to_delete * (self.cols + 1));
-
-        // If we grew down like this, we must be at the bottom.
-        assert(self.viewportIsBottom());
-
         break :deleted rows_to_delete;
     } else 0;
 
diff --git a/src/terminal/circ_buf.zig b/src/terminal/circ_buf.zig
index 59928df1b..1202874f7 100644
--- a/src/terminal/circ_buf.zig
+++ b/src/terminal/circ_buf.zig
@@ -112,6 +112,8 @@ pub fn CircBuf(comptime T: type, comptime default: T) type {
         /// Delete the oldest n values from the buffer. If there are less
         /// than n values in the buffer, it'll delete everything.
         pub fn deleteOldest(self: *Self, n: usize) void {
+            assert(n <= self.storage.len);
+
             // Clear the values back to default
             const slices = self.getPtrSlice(0, n);
             for (slices) |slice| std.mem.set(T, slice, default);
@@ -128,7 +130,8 @@ pub fn CircBuf(comptime T: type, comptime default: T) type {
         /// the end of our buffer. This never "rotates" the buffer because
         /// the offset can only be within the size of the buffer.
         pub fn getPtrSlice(self: *Self, offset: usize, slice_len: usize) [2][]T {
-            assert(slice_len > 0);
+            // Note: this assertion is very important, it hints the compiler
+            // which generates ~10% faster code than without it.
             assert(offset + slice_len <= self.capacity());
 
             // End offset is the last offset (exclusive) for our slice.