diff --git a/OTFbuild/calligra_font_tests.odt b/OTFbuild/calligra_font_tests.odt
index 687354a..bc904ae 100644
Binary files a/OTFbuild/calligra_font_tests.odt and b/OTFbuild/calligra_font_tests.odt differ
diff --git a/OTFbuild/font_builder.py b/OTFbuild/font_builder.py
index db8c411..f7e161c 100644
--- a/OTFbuild/font_builder.py
+++ b/OTFbuild/font_builder.py
@@ -281,7 +281,13 @@ def build_font(assets_dir, output_path, no_bitmap=False, no_features=False):
         if advance == 0:
             x_offset -= g.props.nudge_x * SCALE
 
-        y_offset = -g.props.nudge_y * SCALE
+        # For STACK_DOWN marks (below-base diacritics), negative nudge_y
+        # means "shift content down to below baseline".  The sign convention
+        # is opposite to non-marks where positive nudge_y means shift down.
+        if g.props.stack_where == SC.STACK_DOWN and g.props.write_on_top >= 0:
+            y_offset = g.props.nudge_y * SCALE
+        else:
+            y_offset = -g.props.nudge_y * SCALE
 
         contours = trace_bitmap(g.bitmap, g.props.width)
 
diff --git a/src/net/torvald/terrarumsansbitmap/gdx/TerrarumSansBitmap.kt b/src/net/torvald/terrarumsansbitmap/gdx/TerrarumSansBitmap.kt
index b6bd8af..440684c 100755
--- a/src/net/torvald/terrarumsansbitmap/gdx/TerrarumSansBitmap.kt
+++ b/src/net/torvald/terrarumsansbitmap/gdx/TerrarumSansBitmap.kt
@@ -1250,7 +1250,7 @@ class TerrarumSansBitmap(
                         // set Y pos according to diacritics position
                         when (thisProp.stackWhere) {
                             GlyphProps.STACK_DOWN -> {
-                                posYbuffer[charIndex] = -thisProp.nudgeY + (H_DIACRITICS * stackDownwardCounter + -thisProp.nudgeY) * flipY.toSign()
+                                posYbuffer[charIndex] = (-thisProp.nudgeY + H_DIACRITICS * stackDownwardCounter) * flipY.toSign()
                                 stackDownwardCounter++
                             }
                             GlyphProps.STACK_UP -> {
@@ -1272,11 +1272,11 @@ class TerrarumSansBitmap(
 //                                    dbgprn("lastNonDiacriticChar: ${lastNonDiacriticChar.charInfo()}; stack counter: $stackUpwardCounter")
                             }
                             GlyphProps.STACK_UP_N_DOWN -> {
-                                posYbuffer[charIndex] = -thisProp.nudgeY + (H_DIACRITICS * stackDownwardCounter + -thisProp.nudgeY) * flipY.toSign()
+                                posYbuffer[charIndex] = (-thisProp.nudgeY + H_DIACRITICS * stackDownwardCounter) * flipY.toSign()
                                 stackDownwardCounter++
 
 
-                                posYbuffer[charIndex] = -thisProp.nudgeY + (-H_DIACRITICS * stackUpwardCounter + -thisProp.nudgeY) * flipY.toSign()
+                                posYbuffer[charIndex] = (-thisProp.nudgeY + -H_DIACRITICS * stackUpwardCounter) * flipY.toSign()
                                 // shift down on lowercase if applicable
                                 if (getSheetType(thisChar) in autoShiftDownOnLowercase &&
                                     lastNonDiacriticChar.isLowHeight()) {