diff --git a/src/pygama/math/binned_fitting.py b/src/pygama/math/binned_fitting.py
index 6199575b5..7b4ccc656 100644
--- a/src/pygama/math/binned_fitting.py
+++ b/src/pygama/math/binned_fitting.py
@@ -104,6 +104,7 @@ def fit_binned(
         if isinstance(bounds, dict):
             for key, val in bounds.items():
                 m.limits[key] = val
+                log.debug(f"Set bound for {key} to {val}")
     if fixed is not None:
         for fix in fixed:
             m.fixed[fix] = True
@@ -306,6 +307,9 @@ def gauss_mode_width_max(
     amp_guess = hist[i_0]
     i_0 -= int(np.floor(n_bins / 2))
     i_n = i_0 + n_bins
+    if i_0 < 0 or i_n >= len(hist):
+        msg = f"Fit range exceeds histogram bounds: i_0={i_0}, i_n={i_n}, hist_len={len(hist)}"
+        raise ValueError(msg)
     width_guess = bin_centers[i_n] - bin_centers[i_0]
     vv = None if var is None else var[i_0:i_n]
     guess = (mode_guess, width_guess, amp_guess)
@@ -316,6 +320,11 @@ def gauss_mode_width_max(
         vv,
         guess=guess,
         cost_func=cost_func,
+        bounds={
+            "mu": (bins[i_0], bins[i_n + 1]),
+            "sigma": (0, None),
+            "a": (0, None),
+        },
     )
     if pars[1] < 0:
         pars[1] = -pars[1]