diff --git a/requirements-dev.txt b/requirements-dev.txt
index 7e3ce1d..44a2214 100644
--- a/requirements-dev.txt
+++ b/requirements-dev.txt
@@ -3,13 +3,14 @@ bumpversion==0.5.3
 flake8==3.8.3
 isort==5.4.2
 mypy==0.782
-pytest>=6.0.0,<7.0.0
 pytest-cov==2.10.1
+pytest-mock==3.6.1
+pytest>=6.0.0,<7.0.0
+requests>=2.19.0,<3
 semantic_version>=2.8.1,<3
 sphinx==3.2.1
 sphinx_rtd_theme==0.5.0
 tox==3.19.0
 tqdm>=4.48.0,<5.0.0
 twine==3.2.0
-requests>=2.19.0,<3
 wheel==0.35.1
diff --git a/solcx/main.py b/solcx/main.py
index 5bd3865..a446f1b 100644
--- a/solcx/main.py
+++ b/solcx/main.py
@@ -235,8 +235,11 @@ def compile_files(
     )
 
 
-def _get_combined_json_outputs() -> str:
-    help_str = wrapper.solc_wrapper(help=True)[0].split("\n")
+def _get_combined_json_outputs(solc_binary: Union[Path, str] = None) -> str:
+    if solc_binary is None:
+        solc_binary = get_executable()
+
+    help_str = wrapper.solc_wrapper(solc_binary=solc_binary, help=True)[0].split("\n")
     combined_json_args = next(i for i in help_str if i.startswith("  --combined-json"))
     return combined_json_args.split(" ")[-1]
 
@@ -258,23 +261,23 @@ def _parse_compiler_output(stdoutdata: str) -> Dict:
 
 
 def _compile_combined_json(
-    output_values: Optional[List],
-    solc_binary: Union[str, Path, None],
-    solc_version: Optional[Version],
-    output_dir: Union[str, Path, None],
-    overwrite: Optional[bool],
-    allow_empty: Optional[bool],
+    output_values: Optional[List] = None,
+    solc_binary: Union[str, Path, None] = None,
+    solc_version: Optional[Version] = None,
+    output_dir: Union[str, Path, None] = None,
+    overwrite: Optional[bool] = False,
+    allow_empty: Optional[bool] = False,
     **kwargs: Any,
 ) -> Dict:
 
+    if solc_binary is None:
+        solc_binary = get_executable(solc_version)
+
     if output_values is None:
-        combined_json = _get_combined_json_outputs()
+        combined_json = _get_combined_json_outputs(solc_binary)
     else:
         combined_json = ",".join(output_values)
 
-    if solc_binary is None:
-        solc_binary = get_executable(solc_version)
-
     if output_dir:
         output_dir = Path(output_dir)
         if output_dir.is_file():
diff --git a/tests/main/test_utils.py b/tests/main/test_utils.py
new file mode 100644
index 0000000..7f247ee
--- /dev/null
+++ b/tests/main/test_utils.py
@@ -0,0 +1,14 @@
+import solcx
+import solcx.main
+
+
+def test_get_combined_json_outputs_defaults(mocker, foo_source):
+    # verify we get the correct combined json outputs for different
+    # compiler versions
+    spy = mocker.spy(solcx.main, "_get_combined_json_outputs")
+
+    solcx.compile_source(foo_source, solc_version="0.4.12")
+    assert "function-debug" not in spy.spy_return
+
+    solcx.compile_source(foo_source, solc_version="0.8.9")
+    assert "function-debug" in spy.spy_return