diff --git a/CHANGES b/CHANGES
index 7522faabb5..d10bdfd87d 100644
--- a/CHANGES
+++ b/CHANGES
@@ -1,3 +1,7 @@
+8.1.0-dev.538 | 2025-09-12 09:24:51 -0700
+
+  * for -O gen-standalone-C++, make the presence of uncompilable functions fatal unless -O allow-cond is used (Vern Paxson, Corelight)
+
 8.1.0-dev.536 | 2025-09-12 09:24:12 -0700
 
   * Bump zeekctl for new trace-summary/pysubnettree versions (Tim Wojtulewicz, Corelight)
diff --git a/VERSION b/VERSION
index 9bf8416436..ebb0cc0988 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-8.1.0-dev.536
+8.1.0-dev.538
diff --git a/src/script_opt/CPP/Driver.cc b/src/script_opt/CPP/Driver.cc
index 61b4aca58e..7011a7d315 100644
--- a/src/script_opt/CPP/Driver.cc
+++ b/src/script_opt/CPP/Driver.cc
@@ -25,6 +25,13 @@ CPPCompile::CPPCompile(vector<FuncInfo>& _funcs, std::shared_ptr<ProfileFuncs> _
     }
 
     Compile(report_uncompilable);
+
+    if ( standalone && skipped_uncompilable_func && ! analysis_options.allow_cond ) {
+        reporter->Error(
+            "standalone C++ compilation incomplete due to having to skip some functions; use \"-O allow-cond\" to "
+            "override");
+        exit(1);
+    }
 }
 
 CPPCompile::~CPPCompile() { fclose(write_file); }
@@ -208,6 +215,7 @@ bool CPPCompile::AnalyzeFuncBody(FuncInfo& fi, unordered_set<string>& filenames_
             }
 
             fi.SetSkip(true);
+            skipped_uncompilable_func = true;
         }
     }
 
@@ -252,6 +260,8 @@ bool CPPCompile::AnalyzeFuncBody(FuncInfo& fi, unordered_set<string>& filenames_
         }
 
         not_fully_compilable.insert(f->GetName());
+        skipped_uncompilable_func = true;
+
         return false;
     }
 
diff --git a/src/script_opt/CPP/Driver.h b/src/script_opt/CPP/Driver.h
index 6b17267aa8..d7a266ee7c 100644
--- a/src/script_opt/CPP/Driver.h
+++ b/src/script_opt/CPP/Driver.h
@@ -104,6 +104,9 @@ std::unordered_map<std::string, std::string> hashed_funcs;
 // If true, the generated code should run "standalone".
 bool standalone = false;
 
+// If true, compilation skipped at least one function due to non-compilability.
+bool skipped_uncompilable_func = false;
+
 // Hash over the functions in this compilation.  This is only needed for
 // "seatbelts", to ensure that we can produce a unique hash relating to this
 // compilation (*and* its compilation time, which is why these are "seatbelts"