diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index c7dadb80..5fe62423 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -13,9 +13,9 @@ jobs:
         python-version: ['3.9', '3.10', '3.11', '3.12', '3.13']
 
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v7
     - name: Set up Python ${{ matrix.python-version }}
-      uses: actions/setup-python@v4
+      uses: actions/setup-python@v6
       with:
         python-version: ${{ matrix.python-version }}
     - name: Install dependencies
diff --git a/amitools/vamos/lib/DosLibrary.py b/amitools/vamos/lib/DosLibrary.py
index 789fc2aa..69eb80bb 100644
--- a/amitools/vamos/lib/DosLibrary.py
+++ b/amitools/vamos/lib/DosLibrary.py
@@ -855,12 +855,21 @@ def PutStr(self, ctx, str_ptr):
         log_dos.info("PutStr: %s", show_data)
         return 0  # ok
 
+    @staticmethod
+    def _is_host_stdin(obj):
+        # sys.stdin may be a capture object without a real fd (e.g. under
+        # pytest), where fileno() raises
+        try:
+            return obj.fileno() == sys.stdin.fileno()
+        except (OSError, ValueError, AttributeError):
+            return False
+
     def Flush(self, ctx):
         fh_b_addr = ctx.cpu.r_reg(REG_D1)
         fh = self.file_mgr.get_by_b_addr(fh_b_addr, True)
         fh.flush()
         # remove command line from stdin
-        if fh.obj.fileno() == sys.stdin.fileno():
+        if self._is_host_stdin(fh.obj):
             fh.setbuf(bytearray())
             
         return -1
@@ -986,7 +995,7 @@ def FGets(self, ctx):
         fh = self.file_mgr.get_by_b_addr(fh_b_addr, False)
         
         # Block until input is available
-        if fh.obj.fileno() == sys.stdin.fileno():
+        if self._is_host_stdin(fh.obj):
             while True:
                 ready, _, _ = select.select([fh.obj], [], [], None)
                 if ready:
diff --git a/amitools/vamos/lib/IntuitionLibrary.py b/amitools/vamos/lib/IntuitionLibrary.py
index 3268bdef..7a0929f6 100644
--- a/amitools/vamos/lib/IntuitionLibrary.py
+++ b/amitools/vamos/lib/IntuitionLibrary.py
@@ -69,7 +69,13 @@ def open_lib(self, ctx, open_cnt):
         if self._lib_opened:
             return  # already initialized
 
-        import sdl2
+        # stay headless without sdl2: functions that really render
+        # import sdl2 themselves and fail only when actually used
+        try:
+            import sdl2
+        except ImportError:
+            log_intui.warning("pysdl2 not installed, no display available")
+            return
         sdl2.SDL_Init(sdl2.SDL_INIT_VIDEO | sdl2.SDL_INIT_TIMER)
 
         # open graphics.library
@@ -91,7 +97,7 @@ def open_lib(self, ctx, open_cnt):
         self._lib_opened = True
         
     def close_lib(self, ctx, open_cnt):
-        if open_cnt == 0:
+        if open_cnt == 0 and self._lib_opened:
             # close default screen
             title_addr = self.default_screen.DefaultTitle.get() 
             ctx.cpu.w_reg(REG_A0, self.default_screen.addr)
diff --git a/amitools/vamos/libnative/mgr.py b/amitools/vamos/libnative/mgr.py
index 79c83f9d..764be96e 100644
--- a/amitools/vamos/libnative/mgr.py
+++ b/amitools/vamos/libnative/mgr.py
@@ -10,7 +10,7 @@ def __init__(self, name, load_addr, seglist_baddr, lib_fd=None):
         self.load_addr = load_addr
         self.seglist_baddr = seglist_baddr
         self.lib_fd = lib_fd
-        self.base_addrs = { load_addr: 1 }  # base addr -> num of bases
+        self.base_addrs = {}  # base addr -> num of bases
 
     def __str__(self):
         info = []