diff --git a/gappy/core.pyx b/gappy/core.pyx
index 8a80964..b94ce8d 100644
--- a/gappy/core.pyx
+++ b/gappy/core.pyx
@@ -200,7 +200,7 @@ MakeImmutable(\$GAPPY_ERROUT);
 
 
 # TODO: Change autoload=True by default
-cdef initialize(gap_root=None, gaprc=None, workspace=None, workspace_valid=False, autoload=False):
+cdef initialize(gap_root=None, gap_memory=None, gaprc=None, workspace=None, workspace_valid=False, autoload=False):
     """
     Initialize the GAP library, if it hasn't already been initialized.
 
@@ -225,7 +225,7 @@ cdef initialize(gap_root=None, gaprc=None, workspace=None, workspace_valid=False
     _gap_root = gap_root.encode(_FS_ENCODING, 'surrogateescape')
     argv[2] = _gap_root
 
-    memory_pool = get_gap_memory_pool_size().encode('ascii')
+    memory_pool = get_gap_memory_pool_size().encode('ascii') if gap_memory is None else (str(gap_memory)+'m').encode('ascii')
     argv[3] = '-o'
     argv[4] = memory_pool
     argv[5] = '-s'
@@ -294,6 +294,7 @@ cdef initialize(gap_root=None, gaprc=None, workspace=None, workspace_valid=False
     # Return a dict of the final initialization args (after handling defaults)
     return {
         'gap_root': gap_root,
+				'gap_memory': memory_pool,
         'gaprc': gaprc,
         'workspace': workspace,
         'autoload': autoload
@@ -539,6 +540,9 @@ cdef class Gap:
         interpreter.  This should be the path containing the ``lib/`` and
         ``pkg/`` directories for the standard GAP libraries.  Equivalent to
         the ``-l`` command-line argument to ``gap``.
+    gap_memory : 'int'
+        GAP's memory in megabytes.   Equivalent to the ``o`` command-line 
+        argument to ``gap``.
     gaprc : `str` or `pathlib.Path`
         A GAP "runtime config" file containing GAP commands to run immediately
         upon GAP interpreter startup.  Equivalent to passing a GAP file to
@@ -603,6 +607,7 @@ cdef class Gap:
 
         self._init_kwargs.update(initialize(
             gap_root=self._init_kwargs['gap_root'],
+						gap_memory=self._init_kwargs['gap_memory'],
             gaprc=self._init_kwargs['gaprc'],
             workspace=self._init_kwargs['workspace'],
             workspace_valid=self._init_kwargs['workspace_valid'],
@@ -611,7 +616,7 @@ cdef class Gap:
         _gap_instance = self
         return True
 
-    def __init__(self, gap_root=None, gaprc=None, workspace=None, workspace_valid=False,
+    def __init__(self, gap_root=None, gap_memory=None, gaprc=None, workspace=None, workspace_valid=False,
                  autoinit=False, autoload=False):
         if _gap_is_initialized:
             raise RuntimeError(
@@ -620,6 +625,7 @@ cdef class Gap:
 
         self._init_kwargs.update({
             'gap_root': gap_root,
+						'gap_memory': gap_memory,
             'gaprc': gaprc,
             'workspace': workspace,
             'workspace_valid': workspace_valid,
@@ -837,6 +843,13 @@ cdef class Gap:
 
         return self._init_kwargs.get('gap_root')
 
+    @property
+    def gap_memory(self):
+        """
+        GAP's memory in megabytes.
+        """
+        return self._init_kwargs.get('gap_memory')
+
     @property
     def gaprc(self):
         """
diff --git a/gappy/gap_includes.pxd b/gappy/gap_includes.pxd
index bd8f93e..3f4a2a3 100644
--- a/gappy/gap_includes.pxd
+++ b/gappy/gap_includes.pxd
@@ -129,20 +129,29 @@ cdef extern from "gap/gasman.h" nogil:
     """
     #define GAP_CollectBags(full) CollectBags(0, full)
     """
-    void GAP_MarkBag "MarkBag" (Obj bag)
+    void GAP_MarkBag(Obj bag)
     UInt GAP_CollectBags(UInt full)
 
 
 cdef extern from "gap/io.h" nogil:
-    UInt OpenOutputStream(Obj stream)
-    UInt CloseOutput()
+    """
+    TypOutputFile output = {0};
+    inline UInt GAP_OpenOutputStream(Obj stream) {
+        return OpenOutputStream(&output, stream);
+    }
+    inline UInt GAP_CloseOutput( ) {
+        return CloseOutput(&output);
+    }
+    """
+    UInt GAP_OpenOutputStream(Obj stream)
+    UInt GAP_CloseOutput()
 
 
 # TODO: Replace this with a GAP_MakeStringWithLen from the public API;
 # see https://github.com/gap-system/gap/issues/4211
 cdef extern from "gap/stringobj.h" nogil:
     """
-    static inline Obj GAP_MakeStringWithLen(char *s, size_t len) {
+    inline Obj GAP_MakeStringWithLen(const char *s, size_t len) {
         Obj ret;
         C_NEW_STRING(ret, len, s);
         return ret;
diff --git a/gappy/gapobj.pyx b/gappy/gapobj.pyx
index 0b84ea5..bf45c8d 100644
--- a/gappy/gapobj.pyx
+++ b/gappy/gapobj.pyx
@@ -101,7 +101,7 @@ cdef void capture_stdout(Obj func, Obj obj, Obj out):
         args[0] = out
         args[1] = GAP_True
         stream = GAP_CallFuncArray(output_text_string, 2, args)
-        stream_ok = OpenOutputStream(stream)
+        stream_ok = GAP_OpenOutputStream(stream)
         sig_off()
 
         if not stream_ok:
@@ -111,7 +111,7 @@ cdef void capture_stdout(Obj func, Obj obj, Obj out):
         args[0] = obj
         sig_on()
         GAP_CallFuncArray(func, 1, args)
-        CloseOutput()
+        GAP_CloseOutput()
         sig_off()
     finally:
         sig_GAP_Leave()