diff --git a/src/algorithms/signal_source/adapters/file_source_base.cc b/src/algorithms/signal_source/adapters/file_source_base.cc
index fea84b379..beec41426 100644
--- a/src/algorithms/signal_source/adapters/file_source_base.cc
+++ b/src/algorithms/signal_source/adapters/file_source_base.cc
@@ -185,14 +185,15 @@ FileSourceBase::FileSourceBase(ConfigurationInterface const* configuration, std:
       ,
       is_complex_(false)
 
+      // apparently, MacOS (LLVM) finds 0UL ambiguous with bool, int64_t, uint64_t, int32_t, int16_t, uint16_t,... float, double
       ,
-      header_size_(configuration->property(role + ".header_size"s, 0UL)),
+      header_size_(configuration->property(role + ".header_size"s, size_t(0))),
       seconds_to_skip_(configuration->property(role + ".seconds_to_skip", 0.0)),
       repeat_(configuration->property(role + ".repeat"s, false))
 
       ,
-      samples_(configuration->property(role + ".samples"s, 0UL)),
-      sampling_frequency_(configuration->property(role + ".sampling_frequency"s, 0UL)),
+      samples_(configuration->property(role + ".samples"s, uint64_t(0))),
+      sampling_frequency_(configuration->property(role + ".sampling_frequency"s, int64_t(0))),
       valve_(),
       queue_(queue)
 
diff --git a/src/algorithms/signal_source/adapters/file_source_base.h b/src/algorithms/signal_source/adapters/file_source_base.h
index 61ae97dde..f71ed4df8 100644
--- a/src/algorithms/signal_source/adapters/file_source_base.h
+++ b/src/algorithms/signal_source/adapters/file_source_base.h
@@ -157,7 +157,7 @@ private:
     // beyond its lifetime. Fortunately, the queue is only used to create the valve, so the
     // likelihood of holding a stale pointer is mitigated
     uint64_t samples_;
-    int64_t sampling_frequency_;
+    int64_t sampling_frequency_;  // why is this signed
     gnss_shared_ptr<gr::block> valve_;
     Concurrent_Queue<pmt::pmt_t>* queue_;