diff --git a/brian2/codegen/codeobject.py b/brian2/codegen/codeobject.py
index bb6c71029..038e5cea6 100644
--- a/brian2/codegen/codeobject.py
+++ b/brian2/codegen/codeobject.py
@@ -5,6 +5,7 @@
 import collections
 import copy
 import platform
+from abc import ABC, abstractmethod
 
 from brian2.core.base import weakproxy_with_fallback
 from brian2.core.functions import DEFAULT_FUNCTIONS, Function
@@ -42,7 +43,7 @@ def constant_or_scalar(varname, variable):
         return f"{varname}"
 
 
-class CodeObject(Nameable):
+class CodeObject(Nameable, ABC):
     """
     Executable code object.
 
@@ -105,9 +106,7 @@ def is_available(cls):
         Whether this target for code generation is available. Should use a
         minimal example to check whether code generation works in general.
         """
-        raise NotImplementedError(
-            f"CodeObject class {cls.__name__} is missing an 'is_available' method."
-        )
+        return True
 
     def update_namespace(self):
         """
@@ -117,8 +116,8 @@ def update_namespace(self):
         """
         pass
 
-    def compile_block(self, block):
-        raise NotImplementedError("Implement compile_block method")
+    @abstractmethod
+    def compile_block(self, block): ...
 
     def compile(self):
         for block in ["before_run", "run", "after_run"]:
@@ -130,8 +129,8 @@ def __call__(self, **kwds):
 
         return self.run()
 
-    def run_block(self, block):
-        raise NotImplementedError("Implement run_block method")
+    @abstractmethod
+    def run_block(self, block): ...
 
     def before_run(self):
         """
diff --git a/brian2/codegen/generators/GSL_generator.py b/brian2/codegen/generators/GSL_generator.py
index f5b281e50..f14d16bfe 100644
--- a/brian2/codegen/generators/GSL_generator.py
+++ b/brian2/codegen/generators/GSL_generator.py
@@ -1110,7 +1110,7 @@ def __getattr__(self, item):
     syntax = {
         "end_statement": ";",
         "access_pointer": "->",
-        "start_declare": 'extern "C" ',
+        "start_declare": "",
         "open_function": "\n{",
         "open_struct": "\n{",
         "end_function": "\n}",
@@ -1159,3 +1159,14 @@ def unpack_namespace_single(self, var_obj, in_vector, in_scalar):
                 return f"_GSL_dataholder.{var_obj.name} = {var_obj.name};"
             else:
                 return ""
+
+    def make_function_code(self, lines):
+        # To pass constants that might be used in the function, we need to
+        # add a %CONSTANTS% placeholder that will be replaced by the standalone
+        # device
+        return """
+        // CONSTANTS
+        %CONSTANTS%
+        """ + super().make_function_code(
+            lines
+        )
diff --git a/brian2/codegen/runtime/numpy_rt/numpy_rt.py b/brian2/codegen/runtime/numpy_rt/numpy_rt.py
index d56e8b855..1553f7b55 100644
--- a/brian2/codegen/runtime/numpy_rt/numpy_rt.py
+++ b/brian2/codegen/runtime/numpy_rt/numpy_rt.py
@@ -200,11 +200,6 @@ def __init__(
         )
         self.variables_to_namespace()
 
-    @classmethod
-    def is_available(cls):
-        # no test necessary for numpy
-        return True
-
     def variables_to_namespace(self):
         # Variables can refer to values that are either constant (e.g. dt)
         # or change every timestep (e.g. t). We add the values of the
diff --git a/brian2/codegen/templates.py b/brian2/codegen/templates.py
index 31a6693ba..22f93c73f 100644
--- a/brian2/codegen/templates.py
+++ b/brian2/codegen/templates.py
@@ -144,7 +144,10 @@ def __init__(
         self.templates = LazyTemplateLoader(self.env, extension)
 
     def __getattr__(self, item):
-        return self.templates.get_template(item)
+        try:
+            return self.templates.get_template(item)
+        except KeyError as ex:
+            raise AttributeError from ex  # raise the correct error type for __getattr__
 
     def derive(
         self, package_name, extension=None, env_globals=None, templates_dir="templates"
diff --git a/brian2/devices/cpp_standalone/GSLcodeobject.py b/brian2/devices/cpp_standalone/GSLcodeobject.py
index 6ef49966f..867698668 100644
--- a/brian2/devices/cpp_standalone/GSLcodeobject.py
+++ b/brian2/devices/cpp_standalone/GSLcodeobject.py
@@ -3,13 +3,12 @@
 GNU Scientific Library
 """
 
-from brian2.codegen.codeobject import CodeObject
 from brian2.codegen.generators.cpp_generator import CPPCodeGenerator
 from brian2.codegen.generators.GSL_generator import GSLCPPCodeGenerator
 from brian2.devices.cpp_standalone import CPPStandaloneCodeObject
 
 
-class GSLCPPStandaloneCodeObject(CodeObject):
+class GSLCPPStandaloneCodeObject(CPPStandaloneCodeObject):
     templater = CPPStandaloneCodeObject.templater.derive(
         "brian2.devices.cpp_standalone", templates_dir="templates_GSL"
     )
diff --git a/brian2/stateupdaters/GSL.py b/brian2/stateupdaters/GSL.py
index ca3032fea..671844a8d 100644
--- a/brian2/stateupdaters/GSL.py
+++ b/brian2/stateupdaters/GSL.py
@@ -3,6 +3,7 @@
 provided in the GNU Scientific Library (GSL)
 """
 
+import os
 import sys
 
 from brian2.utils.logger import get_logger
@@ -105,6 +106,9 @@ def get_codeobj_class(self):
                     device.define_macros += [("WIN32", "1"), ("GSL_DLL", "1")]
                 if prefs.GSL.directory is not None:
                     device.include_dirs += [prefs.GSL.directory]
+                    device.library_dirs += [
+                        os.path.abspath(os.path.join(prefs.GSL.directory, "..", "lib"))
+                    ]
             return GSLCPPStandaloneCodeObject
 
         elif isinstance(device, RuntimeDevice):