--- a/browser/app/winlauncher/DllBlocklistWin.cpp
+++ b/browser/app/winlauncher/DllBlocklistWin.cpp
@@ -364,27 +364,28 @@ LauncherVoidResult InitializeDllBlocklis
   // As part of our mitigation of binary tampering, copy our import directory
   // from the original in our executable file.
   LauncherVoidResult importDirRestored = RestoreImportDirectory(
       aFullImagePath, ourExeImage, aChildProcess, ourModule);
   if (importDirRestored.isErr()) {
     return importDirRestored;
   }
 
-  Maybe<nt::PEHeaders::IATThunks> ntdllThunks =
+  Maybe<Span<IMAGE_THUNK_DATA>> ntdllThunks =
       ourExeImage.GetIATThunksForModule("ntdll.dll");
   if (!ntdllThunks) {
     return LAUNCHER_ERROR_FROM_WIN32(ERROR_INVALID_DATA);
   }
 
-  PIMAGE_THUNK_DATA firstIatThunk = ntdllThunks.value().mFirstThunk;
-  SIZE_T iatLength = ntdllThunks.value().Length();
   SIZE_T bytesWritten;
 
   {  // Scope for prot
+    PIMAGE_THUNK_DATA firstIatThunk = ntdllThunks.value().data();
+    SIZE_T iatLength = ntdllThunks.value().LengthBytes();
+
     AutoVirtualProtect prot(firstIatThunk, iatLength, PAGE_READWRITE,
                             aChildProcess);
     if (!prot) {
       return LAUNCHER_ERROR_FROM_MOZ_WINDOWS_ERROR(prot.GetError());
     }
 
     ok = !!::WriteProcessMemory(aChildProcess, firstIatThunk, firstIatThunk,
                                 iatLength, &bytesWritten);

--- a/mozglue/misc/NativeNt.h
+++ b/mozglue/misc/NativeNt.h
@@ -407,29 +407,18 @@ class MOZ_RAII PEHeaders final {
 
       // curImpDesc now points to the IAT for the module we're interested in
       return curImpDesc;
     }
 
     return nullptr;
   }
 
-  struct IATThunks {
-    IATThunks(PIMAGE_THUNK_DATA aFirstThunk, ptrdiff_t aNumThunks)
-        : mFirstThunk(aFirstThunk), mNumThunks(aNumThunks) {}
-
-    size_t Length() const {
-      return size_t(mNumThunks) * sizeof(IMAGE_THUNK_DATA);
-    }
-
-    PIMAGE_THUNK_DATA mFirstThunk;
-    ptrdiff_t mNumThunks;
-  };
-
-  Maybe<IATThunks> GetIATThunksForModule(const char* aModuleNameASCII) {
+  Maybe<Span<IMAGE_THUNK_DATA>> GetIATThunksForModule(
+      const char* aModuleNameASCII) {
     PIMAGE_IMPORT_DESCRIPTOR impDesc = GetIATForModule(aModuleNameASCII);
     if (!impDesc) {
       return Nothing();
     }
 
     auto firstIatThunk =
         this->template RVAToPtr<PIMAGE_THUNK_DATA>(impDesc->FirstThunk);
     if (!firstIatThunk) {
@@ -437,18 +426,17 @@ class MOZ_RAII PEHeaders final {
     }
 
     // Find the length by iterating through the table until we find a null entry
     PIMAGE_THUNK_DATA curIatThunk = firstIatThunk;
     while (IsValid(curIatThunk)) {
       ++curIatThunk;
     }
 
-    ptrdiff_t thunkCount = curIatThunk - firstIatThunk;
-    return Some(IATThunks(firstIatThunk, thunkCount));
+    return Some(MakeSpan(firstIatThunk, curIatThunk));
   }
 
   /**
    * Resources are stored in a three-level tree. To locate a particular entry,
    * you must supply a resource type, the resource id, and then the language id.
    * If aLangId == 0, we just resolve the first entry regardless of language.
    */
   template <typename T>

--- a/mozglue/tests/TestNativeNt.cpp
+++ b/mozglue/tests/TestNativeNt.cpp
@@ -146,10 +146,27 @@ int main(int argc, char* argv[]) {
   if (version != expectedVersion) {
     printf(
         "TEST-FAILED | NativeNt | kernel32.dll's detected version "
         "(0x%016llX) does not match expected version (0x%016llX)\n",
         version, expectedVersion);
     return 1;
   }
 
+  Maybe<Span<IMAGE_THUNK_DATA>> iatThunks =
+      k32headers.GetIATThunksForModule("kernel32.dll");
+  if (iatThunks) {
+    printf(
+        "TEST-FAILED | NativeNt | Detected the IAT thunk for kernel32 "
+        "in kernel32.dll\n");
+    return 1;
+  }
+
+  iatThunks = k32headers.GetIATThunksForModule("ntdll.dll");
+  if (!iatThunks) {
+    printf(
+        "TEST-FAILED | NativeNt | Unable to find the IAT thunk for "
+        "ntdll.dll in kernel32.dll\n");
+    return 1;
+  }
+
   return 0;
 }