diff --git a/CHANGELOG.md b/CHANGELOG.md
index a7f27bc1..c711b664 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -109,6 +109,8 @@
 * A multi-column character that does not fit on the current line is
   now printed on the next line, instead of only printing half the
   character.
+* Font size can no longer be reduced to negative values
+  (https://codeberg.org/dnkl/foot/issues/38).
 
 
 ### Security
diff --git a/csi.c b/csi.c
index fc6db974..fe102ada 100644
--- a/csi.c
+++ b/csi.c
@@ -338,8 +338,10 @@ csi_dispatch(struct terminal *term, uint8_t final)
                 LOG_DBG("REP: '%C' %d times", term->vt.last_printed, count);
 
                 const int width = wcwidth(term->vt.last_printed);
-                for (int i = 0; i < count; i++)
-                    term_print(term, term->vt.last_printed, width);
+                if (width > 0) {
+                    for (int i = 0; i < count; i++)
+                        term_print(term, term->vt.last_printed, width);
+                }
             }
             break;
 
diff --git a/sixel.c b/sixel.c
index 7d4b3d38..7dab1fcc 100644
--- a/sixel.c
+++ b/sixel.c
@@ -113,13 +113,33 @@ verify_sixel_list_order(const struct terminal *term)
 {
 #if defined(_DEBUG)
     int prev_row = INT_MAX;
+    int prev_col = -1;
+    int prev_col_count = 0;
 
     tll_foreach(term->grid->sixel_images, it) {
         int row = rebase_row(term, it->item.pos.row + it->item.rows - 1);
-        assert(row < prev_row);
-        if (row >= prev_row)
+        int col = it->item.pos.col;
+        int col_count = it->item.cols;
+
+        assert(row <= prev_row);
+        if (row > prev_row)
             return false;
+
+        if (row == prev_row) {
+            /* Allowed to be on the same row only if their columns
+             * don't overlap */
+
+            assert(col + col_count <= prev_col ||
+                   prev_col + prev_col_count <= col);
+
+            if (!(col + col_count <= prev_col ||
+                  prev_col + prev_col_count <= col))
+                return false;
+        }
+
         prev_row = row;
+        prev_col = col;
+        prev_col_count = col_count;
     }
 #endif
     return true;
diff --git a/terminal.c b/terminal.c
index c720aea4..86672f06 100644
--- a/terminal.c
+++ b/terminal.c
@@ -1432,7 +1432,7 @@ term_font_size_adjust(struct terminal *term, double amount)
             old_pt_size = term->font_sizes[i].px_size * 72. / dpi;
         }
 
-        term->font_sizes[i].pt_size = old_pt_size + amount;
+        term->font_sizes[i].pt_size = fmax(old_pt_size + amount, 0);
         term->font_sizes[i].px_size = -1;
     }
 
@@ -2307,12 +2307,15 @@ print_linewrap(struct terminal *term)
     }
 
     term->grid->cursor.lcf = false;
-    if (term->grid->cursor.point.row == term->scroll_region.end - 1)
+
+    const int row = term->grid->cursor.point.row;
+
+    if (row == term->scroll_region.end - 1)
         term_scroll(term, 1);
     else {
-        assert(term->grid->cursor.point.row < term->scroll_region.end - 1);
-        term->grid->cursor.point.row++;
-        term->grid->cur_row = grid_row(term->grid, term->grid->cursor.point.row);
+        const int new_row = min(row + 1, term->rows - 1);
+        term->grid->cursor.point.row = new_row;
+        term->grid->cur_row = grid_row(term->grid, new_row);
     }
 
     term->grid->cursor.point.col = 0;
@@ -2353,8 +2356,7 @@ print_spacer(struct terminal *term, int col)
 void
 term_print(struct terminal *term, wchar_t wc, int width)
 {
-    if (unlikely(width <= 0))
-        return;
+    assert(width > 0);
 
     print_linewrap(term);
     print_insert(term, width);
diff --git a/vt.c b/vt.c
index 618611c6..f25f26be 100644
--- a/vt.c
+++ b/vt.c
@@ -223,6 +223,8 @@ action_print(struct terminal *term, uint8_t c)
         L'│', L'≤', L'≥', L'π', L'≠', L'£', L'·',       /* x - ~ */
     };
 
+    assert(wcwidth(c) == 1);
+
     if (unlikely(term->charsets.set[term->charsets.selected] == CHARSET_GRAPHIC) &&
         c >= 0x60 && c <= 0x7e)
     {
@@ -540,15 +542,12 @@ action_utf8_print(struct terminal *term, wchar_t wc)
         if (!term->grid->cursor.lcf)
             base_col--;
 
+        while (row->cells[base_col].wc == CELL_MULT_COL_SPACER && base_col > 0)
+            base_col--;
+
         assert(base_col >= 0 && base_col < term->cols);
         wchar_t base = row->cells[base_col].wc;
 
-        /* Handle double-column glyphs */
-        if (base == 0 && base_col > 0) {
-            base_col--;
-            base = row->cells[base_col].wc;
-        }
-
         const struct composed *composed =
             (base >= CELL_COMB_CHARS_LO &&
              base < (CELL_COMB_CHARS_LO + term->composed_count))
@@ -664,7 +663,8 @@ action_utf8_print(struct terminal *term, wchar_t wc)
         }
     }
 
-    term_print(term, wc, width);
+    if (width > 0)
+        term_print(term, wc, width);
 }
 
 static void
@@ -742,7 +742,8 @@ state_ground_switch(struct terminal *term, uint8_t data)
     case 0x19:
     case 0x1c ... 0x1f:                                  action_execute(term, data);                                       return STATE_GROUND;
 
-    case 0x20 ... 0x7f:                                  action_print(term, data);                                         return STATE_GROUND;
+    /* modified from 0x20..0x7f to 0x20..0x7e, since 0x7f is DEL, which is a zero-width character */
+    case 0x20 ... 0x7e:                                  action_print(term, data);                                         return STATE_GROUND;
 
     case 0xc2 ... 0xdf:                                  action_utf8_21(term, data);                                       return STATE_UTF8_21;
     case 0xe0 ... 0xef:                                  action_utf8_31(term, data);                                       return STATE_UTF8_31;