--- a/layout/style/nsComputedDOMStyle.cpp
+++ b/layout/style/nsComputedDOMStyle.cpp
@@ -5485,46 +5485,33 @@ already_AddRefed<CSSValue>
 nsComputedDOMStyle::DoGetMaxWidth()
 {
   RefPtr<nsROCSSPrimitiveValue> val = new nsROCSSPrimitiveValue;
   SetValueToCoord(val, StylePosition()->mMaxWidth, true,
                   nullptr, nsCSSProps::kWidthKTable);
   return val.forget();
 }
 
+/**
+ * This function indicates whether we should return "auto" as the
+ * getComputedStyle() result for the (default) "min-width: auto" and
+ * "min-height: auto" CSS values.
+ *
+ * As of this writing, the CSS Sizing draft spec says this "auto" value
+ * *always* computes to itself.  However, for now, we only make it compute to
+ * itself for grid and flex items (the containers where "auto" has special
+ * significance), because those are the only areas where the CSSWG has actually
+ * resolved on this "computes-to-itself" behavior. For elements in other sorts
+ * of containers, this function returns false, which will make us resolve
+ * "auto" to 0.
+ */
 bool
 nsComputedDOMStyle::ShouldHonorMinSizeAutoInAxis(PhysicalAxis aAxis)
 {
-  // A {flex,grid} item's min-{width|height} "auto" value gets special
-  // treatment in getComputedStyle().
-  // https://drafts.csswg.org/css-flexbox-1/#valdef-min-width-auto
-  // https://drafts.csswg.org/css-grid/#min-size-auto
-  // In most cases, "min-{width|height}: auto" is mapped to "0px", unless
-  // we're a flex item (and the min-size is in the flex container's main
-  // axis), or we're a grid item, AND we also have overflow:visible.
-
-  // Note: We only need to bother checking one "overflow" subproperty for
-  // "visible", because a non-"visible" value in either axis would force the
-  // other axis to also be non-"visible" as well.
-
-  if (mOuterFrame) {
-    nsIFrame* containerFrame = mOuterFrame->GetParent();
-    if (containerFrame &&
-        StyleDisplay()->mOverflowX == NS_STYLE_OVERFLOW_VISIBLE) {
-      if (containerFrame->IsFlexContainerFrame() &&
-          (static_cast<nsFlexContainerFrame*>(containerFrame)->IsHorizontal() ==
-           (aAxis == eAxisHorizontal))) {
-        return true;
-      }
-      if (containerFrame->IsGridContainerFrame()) {
-        return true;
-      }
-    }
-  }
-  return false;
+  return mOuterFrame && mOuterFrame->IsFlexOrGridItem();
 }
 
 already_AddRefed<CSSValue>
 nsComputedDOMStyle::DoGetMinHeight()
 {
   RefPtr<nsROCSSPrimitiveValue> val = new nsROCSSPrimitiveValue;
   nsStyleCoord minHeight = StylePosition()->mMinHeight;
 

--- a/layout/style/test/test_computed_style_min_size_auto.html
+++ b/layout/style/test/test_computed_style_min_size_auto.html
@@ -84,30 +84,26 @@ function checkElemMinSizes(aElemId,
 // This function goes through all the elements we're interested in
 // and checks their computed min-sizes against expected values,
 // farming out each per-element job to checkElemMinSizes.
 function checkAllTheMinSizes() {
   // This is the normal part -- generally, the default value of "min-width"
   // and "min-height" (auto) computes to "0px".
   checkElemMinSizes("block-item", "0px", "0px");
 
-  // ...but for a flex item in a horizontal flex container, "min-width: auto"
-  // computes to "auto".
-  checkElemMinSizes("horizontal-flex-item", "auto", "0px");
-  checkElemMinSizes("horizontal-flex-item-OH", "0px", "0px");
-
-  // ...and for a flex item in a vertical flex container, "min-height: auto"
-  // computes to "auto".
-  checkElemMinSizes("vertical-flex-item", "0px", "auto");
-  checkElemMinSizes("vertical-flex-item-OH", "0px", "0px");
-
-  // ...and for a grid item, "min-width: auto" and min-height both
-  // compute to "auto".
-  checkElemMinSizes("grid-item", "auto", "auto");
-  checkElemMinSizes("grid-item-OH", "0px", "0px");
+  // ...but for a flex item or grid item, "min-width: auto" and
+  // "min-height: auto" both compute to "auto" (even in cases where
+  // we know it'll actually resolve to 0 in layout, like for example
+  // when the item has "overflow:hidden").
+  checkElemMinSizes("horizontal-flex-item",    "auto", "auto");
+  checkElemMinSizes("horizontal-flex-item-OH", "auto", "auto");
+  checkElemMinSizes("vertical-flex-item",      "auto", "auto");
+  checkElemMinSizes("vertical-flex-item-OH",   "auto", "auto");
+  checkElemMinSizes("grid-item",               "auto", "auto");
+  checkElemMinSizes("grid-item-OH",            "auto", "auto");
 }
 
 // Main test function
 function main() {
   // First: check that min-sizes are what we expect, with min-size properties
   // at their initial value.
   checkAllTheMinSizes();