diff --git a/bgfilter/alpha_post.py b/bgfilter/alpha_post.py
index 5151c32..72911fa 100644
--- a/bgfilter/alpha_post.py
+++ b/bgfilter/alpha_post.py
@@ -85,3 +85,24 @@ def clean_alpha(
             out[hole & (trimap == 255)] = 1.0
 
     return enforce_trimap(out, trimap)
+
+
+def fill_seg_dropouts(
+    alpha: np.ndarray, seg_mask: np.ndarray, settings: AlphaPostSettings
+) -> np.ndarray:
+    """Rescue alpha where ViTMatte dropped a region the semantic mask asserts.
+
+    Green-contaminated wisps are nearly the background colour, so ViTMatte (a
+    contrast-based matter) cuts them even though BiRefNet still sees them. Where
+    ViTMatte's alpha is near zero but the segmentation mask is confidently
+    foreground, restore a faint alpha from the mask. Limited to those dropouts so
+    ViTMatte's sharper edges elsewhere are untouched, and gated by seg_min so the
+    mask's faint halo and the finger gap (low mask) are not filled.
+    """
+    if not settings.seg_fill:
+        return alpha
+    out = alpha.astype(np.float32).copy()
+    rescued = settings.seg_fill_strength * np.clip(seg_mask, 0.0, 1.0)
+    dropout = (out < settings.seg_fill_alpha_max) & (seg_mask >= settings.seg_fill_seg_min)
+    out[dropout] = np.maximum(out[dropout], rescued[dropout])
+    return np.clip(out, 0.0, 1.0)
diff --git a/bgfilter/pipeline.py b/bgfilter/pipeline.py
index 7b9ff8f..e346670 100644
--- a/bgfilter/pipeline.py
+++ b/bgfilter/pipeline.py
@@ -6,7 +6,12 @@ from pathlib import Path
 
 import numpy as np
 
-from .alpha_post import clean_alpha, enforce_trimap, suppress_alpha_by_chroma
+from .alpha_post import (
+    clean_alpha,
+    enforce_trimap,
+    fill_seg_dropouts,
+    suppress_alpha_by_chroma,
+)
 from .chroma import compute_bg_confidence
 from .despill import despill_green
 from .foreground import estimate_foreground_rgb
@@ -86,6 +91,8 @@ def _run_image(
     alpha = enforce_trimap(alpha, trimap)
     alpha = suppress_alpha_by_chroma(alpha, bg_confidence, trimap, settings.alpha_post)
     alpha = clean_alpha(alpha, trimap, settings.alpha_post)
+    if seg_mask is not None:
+        alpha = fill_seg_dropouts(alpha, seg_mask, settings.alpha_post)
     foreground = estimate_foreground_rgb(
         rgb, alpha, bg_confidence, model, settings.foreground
     )
diff --git a/bgfilter/settings.py b/bgfilter/settings.py
index a9e1250..20e5508 100644
--- a/bgfilter/settings.py
+++ b/bgfilter/settings.py
@@ -42,6 +42,12 @@ class AlphaPostSettings:
     chroma_suppress_bg_low: float = 0.35
     chroma_suppress_bg_high: float = 0.80
     chroma_suppress_strength: float = 1.0
+    # Segmentation dropout-fill: rescue alpha where ViTMatte cut a region the
+    # semantic mask asserts is foreground (green-contaminated wisps it cannot see).
+    seg_fill: bool = True
+    seg_fill_alpha_max: float = 0.10
+    seg_fill_seg_min: float = 0.10
+    seg_fill_strength: float = 0.70
 
 
 @dataclass(frozen=True)
diff --git a/configs/default.yaml b/configs/default.yaml
index 13dc8f2..a1b3c47 100644
--- a/configs/default.yaml
+++ b/configs/default.yaml
@@ -23,6 +23,10 @@ alpha_post:
   chroma_suppress_bg_low: 0.35
   chroma_suppress_bg_high: 0.80
   chroma_suppress_strength: 1.0
+  seg_fill: true
+  seg_fill_alpha_max: 0.10
+  seg_fill_seg_min: 0.10
+  seg_fill_strength: 0.70
 
 foreground:
   enabled: true