diff --git a/modules/extras.py b/modules/extras.py
index b8ebc6193..15de033a0 100644
--- a/modules/extras.py
+++ b/modules/extras.py
@@ -150,6 +150,12 @@ def run_modelmerger(primary_model_name, secondary_model_name, interp_method, int
         alpha = alpha * alpha * (3 - (2 * alpha))
         return theta0 + ((theta1 - theta0) * alpha)
 
+    # Inverse Smoothstep (https://en.wikipedia.org/wiki/Smoothstep)
+    def inv_sigmoid(theta0, theta1, alpha):
+        import math
+        alpha = 0.5 - math.sin(math.asin(1.0 - 2.0 * alpha) / 3.0)
+        return theta0 + ((theta1 - theta0) * alpha)
+
     if os.path.exists(primary_model_name):
         primary_model_filename = primary_model_name
         primary_model_name = os.path.splitext(os.path.basename(primary_model_name))[0]
@@ -174,6 +180,7 @@ def run_modelmerger(primary_model_name, secondary_model_name, interp_method, int
     theta_funcs = {
         "Weighted Sum": weighted_sum,
         "Sigmoid": sigmoid,
+        "Inverse Sigmoid": inv_sigmoid
     }
     theta_func = theta_funcs[interp_method]
 
diff --git a/modules/ui.py b/modules/ui.py
index 7db8edbd8..f5d766134 100644
--- a/modules/ui.py
+++ b/modules/ui.py
@@ -864,7 +864,7 @@ def create_ui(txt2img, img2img, run_extras, run_pnginfo, run_modelmerger):
                     primary_model_name   = gr.Dropdown(ckpt_name_list, elem_id="modelmerger_primary_model_name", label="Primary Model Name")
                     secondary_model_name = gr.Dropdown(ckpt_name_list, elem_id="modelmerger_secondary_model_name", label="Secondary Model Name")
                 interp_amount = gr.Slider(minimum=0.0, maximum=1.0, step=0.05, label='Interpolation Amount', value=0.3)
-                interp_method = gr.Radio(choices=["Weighted Sum", "Sigmoid"], value="Weighted Sum", label="Interpolation Method")
+                interp_method = gr.Radio(choices=["Weighted Sum", "Sigmoid", "Inverse Sigmoid"], value="Weighted Sum", label="Interpolation Method")
                 submit = gr.Button(elem_id="modelmerger_merge", label="Merge", variant='primary')
             
             with gr.Column(variant='panel'):