diff --git a/src/panel_splitjs/base.py b/src/panel_splitjs/base.py
index de9bc83..5f56156 100644
--- a/src/panel_splitjs/base.py
+++ b/src/panel_splitjs/base.py
@@ -33,7 +33,7 @@ def _validate(self, val):
             return
         if self.length is not None and isinstance(val, tuple) and len(val) != self.length:
             raise ValueError(f"Size parameter {self.name!r} must have length {self.length}")
-        if not (isinstance(val, (int, float)) or (isinstance(val, tuple) and all(isinstance(v, (int, float)) for v in val))):
+        if not (isinstance(val, (int, float)) or (isinstance(val, tuple) and all(isinstance(v, (int, float)) or v is None for v in val))):
             raise ValueError(f"Size parameter {self.name!r} only takes int or float values")
 
 
diff --git a/src/panel_splitjs/dist/css/splitjs.css b/src/panel_splitjs/dist/css/splitjs.css
index cbd5171..6e1cbd5 100644
--- a/src/panel_splitjs/dist/css/splitjs.css
+++ b/src/panel_splitjs/dist/css/splitjs.css
@@ -39,10 +39,6 @@
   width: 100%;
 }
 
-/* Ensure buttons stay visible even when panels are collapsed */
-.split.single-split > div:first-child {
-  min-width: 0 !important; /* Override any minimum width */
-}
 
 .split.single-split > div:nth-child(2) {
   overflow: visible !important; /* Ensure buttons remain visible */
diff --git a/src/panel_splitjs/models/split.js b/src/panel_splitjs/models/split.js
index 3edcc57..64e2b52 100644
--- a/src/panel_splitjs/models/split.js
+++ b/src/panel_splitjs/models/split.js
@@ -7,10 +7,32 @@ export function render({ model, el }) {
   split_div.className = `split single-split ${model.orientation}`
   split_div.classList.add("loading")
 
+  const [left_min, right_min] = Array.isArray(model.min_size) ? model.min_size : [model.min_size, model.min_size]
+
+  if (model.orientation === "horizontal") {
+    split_div.style.minWidth = `${left_min + right_min + 8}px`
+  } else {
+    split_div.style.minHeight = `${left_min + right_min + 8}px`
+  }
+
   const split0 = document.createElement("div")
   split0.className = "split-panel"
+  if (left_min) {
+    if (model.orientation === "horizontal") {
+      split0.style.minWidth = `${left_min}px`
+    } else {
+      split0.style.minHeight = `${left_min}px`
+    }
+  }
   const split1 = document.createElement("div")
   split1.className = "split-panel"
+  if (right_min) {
+    if (model.orientation === "horizontal") {
+      split1.style.minWidth = `${right_min}px`
+    } else {
+      split1.style.minHeight = `${right_min}px`
+    }
+  }
   split_div.append(split0, split1)
 
   const left_content_wrapper = document.createElement("div")
@@ -63,7 +85,6 @@ export function render({ model, el }) {
         new_sizes = [0, 100]
         left_click_count = 0
       }
-      model.collapsed = is_collapsed
       sync_ui(new_sizes, true)
     })
 
@@ -80,7 +101,6 @@ export function render({ model, el }) {
         new_sizes = [100, 0]
         right_click_count = 0
       }
-      model.collapsed = is_collapsed
       sync_ui(new_sizes, true)
     })
   }
@@ -123,8 +143,8 @@ export function render({ model, el }) {
   })
 
   function sync_ui(sizes = null, resize = false) {
-    const left_panel_hidden = sizes ? sizes[0] <= COLLAPSED_SIZE : false
-    const right_panel_hidden = sizes ? sizes[1] <= COLLAPSED_SIZE : false
+    const left_panel_hidden = sizes ? ((sizes[0] <= COLLAPSED_SIZE) && (left_min < COLLAPSED_SIZE)) : false
+				       const right_panel_hidden = sizes ? ((sizes[1] <= COLLAPSED_SIZE) && (right_min < COLLAPSED_SIZE)) : false
 
     let [ls, rs] = sizes
     if (right_panel_hidden) {
@@ -143,8 +163,8 @@ export function render({ model, el }) {
     if (resize) {
       split_instance.setSizes([ls, rs])
       sizes = [ls, rs]
-      model.sizes = [ls, rs]
       window.dispatchEvent(new Event('resize'))
+      requestAnimationFrame(() => { model.sizes = split_instance.getSizes() })
     }
   }
 
@@ -153,6 +173,7 @@ export function render({ model, el }) {
       return
     }
     sizes = model.sizes
+    model.collapsed = (1-sizes[0]) >= 0 ? 0 : (1-sizes[1]) >= 0 ? 1 : null
     sync_ui(sizes, true)
   })
 
diff --git a/tests/test_ui.py b/tests/test_ui.py
index e996705..7cd222b 100644
--- a/tests/test_ui.py
+++ b/tests/test_ui.py
@@ -3,6 +3,7 @@
 pytest.importorskip('playwright')
 
 from panel.tests.util import serve_component, wait_until
+from panel.pane import Markdown
 from panel.widgets import Button
 from panel_splitjs import MultiSplit, Split
 from playwright.sync_api import expect
@@ -26,6 +27,69 @@ def test_split(page, orientation):
     expect(page.locator('.split-panel').last).to_have_attribute('style', f'{attr}: calc(50% - 4px);')
 
 
+@pytest.mark.parametrize('orientation', ['horizontal', 'vertical'])
+def test_split_min_size_and_total_width(page, orientation):
+    split = Split(
+        Markdown("## Left Panel\nContent here", width=150, margin=25),
+        Markdown("## Right Panel\nMore content", width=150, margin=25),
+        sizes=(50, 50),  # Equal sizing initially
+        min_size=300,    # Minimum 300px for each panel
+        show_buttons=True,
+        orientation=orientation
+    )
+    serve_component(page, split)
+
+    # Check total width/height is 608px
+    attr = "width" if orientation == "horizontal" else "height"
+    expect(page.locator(".single-split")).to_have_attribute("style", f"min-{attr}: 608px;")
+
+    # Collapse left panel using the left button
+    left_button = page.locator(".toggle-button-left,.toggle-button-up").first
+    left_button.click()
+    # Wait to ensure UI has updated; the left panel should not collapse below min_size=300px,
+    # so after collapse, its width/height should be 300px.
+    expect(page.locator(".split-panel").first).to_have_css(attr, "300px")
+
+    # Collapse right panel using the right button
+    right_button = page.locator(".toggle-button-right,.toggle-button-down").first
+    right_button.click()
+    # Wait, then check right does not collapse below 300px
+    expect(page.locator(".split-panel").last).to_have_css(attr, "300px")
+
+@pytest.mark.parametrize('orientation', ['horizontal', 'vertical'])
+def test_split_min_size_one_side(page, orientation):
+    # Only first panel has a min_size of 300px, second is unconstrained
+    split = Split(
+        Markdown("## Left", width=150),
+        Markdown("## Right", width=150),
+        sizes=(50, 50),
+        min_size=(300, None),
+        show_buttons=True,
+        orientation=orientation,
+        width=600 if orientation == "horizontal" else None,
+        height=600 if orientation == "vertical" else None
+    )
+    serve_component(page, split)
+
+    attr = "width" if orientation == "horizontal" else "height"
+    # The minimum size style is still 308px (because None becomes 0, so 300+0+8)
+    expect(page.locator(".single-split")).to_have_attribute("style", f"min-{attr}: 308px;")
+
+    # Collapse left panel -- it should not collapse below 300px
+    left_button = page.locator(".toggle-button-left,.toggle-button-up").first
+    left_button.click()
+    expect(page.locator(".split-panel").first).to_have_css(attr, "300px")
+
+    # Collapse right panel -- right can collapse to minimum, which is 5px (default collapsed size)
+    right_button = page.locator(".toggle-button-right,.toggle-button-down").first
+    right_button.click()
+    # The right panel should be collapsed to zero
+    expect(page.locator(".split-panel").last).to_have_css(attr, "0px")
+
+    # The left panel still stays at its min_size
+    expect(page.locator(".split-panel").first).to_have_css(attr, "592px")
+
+
 def test_split_sizes(page):
     split = Split(Button(name='Left'), Button(name='Right'), sizes=(40, 60), width=400)
     serve_component(page, split)
@@ -64,13 +128,13 @@ def test_split_collapsed_programmatically(page):
     split.collapsed = 0
     expect(page.locator('.split-panel').first).to_have_attribute('style', 'width: calc(1% - 4px);')
     expect(page.locator('.split-panel').last).to_have_attribute('style', 'width: calc(99% - 4px);')
-    wait_until(lambda: split.sizes == (0, 100), page)
+    wait_until(lambda: split.sizes == (1, 99), page)
     wait_until(lambda: split.collapsed == 0, page)
 
     split.collapsed = 1
     expect(page.locator('.split-panel').first).to_have_attribute('style', 'width: calc(99% - 4px);')
     expect(page.locator('.split-panel').last).to_have_attribute('style', 'width: calc(1% - 4px);')
-    wait_until(lambda: split.sizes == (100, 0), page)
+    wait_until(lambda: split.sizes == (99, 1), page)
     wait_until(lambda: split.collapsed == 1, page)
 
     split.collapsed = None
@@ -104,7 +168,7 @@ def test_split_click_toggle_button(page, orientation):
     page.locator(f'.toggle-button-{btn1}').click()
     expect(page.locator('.split-panel').first).to_have_attribute('style', f'{attr}: calc(1% - 4px);')
     expect(page.locator('.split-panel').last).to_have_attribute('style', f'{attr}: calc(99% - 4px);')
-    wait_until(lambda: split.sizes == (0, 100), page)
+    wait_until(lambda: split.sizes == (1, 99), page)
     wait_until(lambda: split.collapsed == 0, page)
 
     page.locator(f'.toggle-button-{btn2}').click()
@@ -116,7 +180,7 @@ def test_split_click_toggle_button(page, orientation):
     page.locator(f'.toggle-button-{btn2}').click()
     expect(page.locator('.split-panel').first).to_have_attribute('style', f'{attr}: calc(99% - 4px);')
     expect(page.locator('.split-panel').last).to_have_attribute('style', f'{attr}: calc(1% - 4px);')
-    wait_until(lambda: split.sizes == (100, 0), page)
+    wait_until(lambda: split.sizes == (99, 1), page)
     wait_until(lambda: split.collapsed == 1, page)