diff --git a/layout/style/nsStyleContext.cpp b/layout/style/nsStyleContext.cpp
index 8801102e431..106f2e0d89f 100644
--- a/layout/style/nsStyleContext.cpp
+++ b/layout/style/nsStyleContext.cpp
@@ -32,6 +32,35 @@ using namespace mozilla;
 
 //----------------------------------------------------------------------
 
+#ifdef DEBUG
+
+// Check that the style struct IDs are in the same order as they are
+// in nsStyleStructList.h, since when we set up the IDs, we include
+// the inherited and reset structs spearately from nsStyleStructList.h
+enum DebugStyleStruct {
+#define STYLE_STRUCT(name, checkdata_cb) eDebugStyleStruct_##name,
+#include "nsStyleStructList.h"
+#undef STYLE_STRUCT
+};
+
+#define STYLE_STRUCT(name, checkdata_cb) \
+  static_assert(static_cast<int>(eDebugStyleStruct_##name) == \
+                  static_cast<int>(eStyleStruct_##name), \
+                "Style struct IDs are not declared in order?");
+#include "nsStyleStructList.h"
+#undef STYLE_STRUCT
+
+const uint32_t nsStyleContext::sDependencyTable[] = {
+#define STYLE_STRUCT(name, checkdata_cb)
+#define STYLE_STRUCT_DEP(dep) NS_STYLE_INHERIT_BIT(dep) |
+#define STYLE_STRUCT_END() 0,
+#include "nsStyleStructList.h"
+#undef STYLE_STRUCT
+#undef STYLE_STRUCT_DEP
+#undef STYLE_STRUCT_END
+};
+
+#endif
 
 nsStyleContext::nsStyleContext(nsStyleContext* aParent,
                                nsIAtom* aPseudoTag,
@@ -54,6 +83,12 @@ nsStyleContext::nsStyleContext(nsStyleContext* aParent,
                 "pseudo element bits no longer fit in a uint64_t");
   MOZ_ASSERT(aRuleNode);
 
+#ifdef DEBUG
+  static_assert(MOZ_ARRAY_LENGTH(nsStyleContext::sDependencyTable)
+                  == nsStyleStructID_Length,
+                "Number of items in dependency table doesn't match IDs");
+#endif
+
   mNextSibling = this;
   mPrevSibling = this;
   if (mParent) {
diff --git a/layout/style/nsStyleContext.h b/layout/style/nsStyleContext.h
index 91945e93dcd..61738e3d9d4 100644
--- a/layout/style/nsStyleContext.h
+++ b/layout/style/nsStyleContext.h
@@ -517,6 +517,17 @@ private:
   uint64_t                mBits; // Which structs are inherited from the
                                  // parent context or owned by mRuleNode.
   uint32_t                mRefCnt;
+
+#ifdef DEBUG
+  static bool DependencyAllowed(nsStyleStructID aOuterSID,
+                                nsStyleStructID aInnerSID)
+  {
+    return !!(sDependencyTable[aOuterSID] &
+              nsCachedStyleData::GetBitForSID(aInnerSID));
+  }
+
+  static const uint32_t sDependencyTable[];
+#endif
 };
 
 already_AddRefed<nsStyleContext>