diff --git a/cpu.cpp b/cpu.cpp
index 5a938ca..356c0d4 100644
--- a/cpu.cpp
+++ b/cpu.cpp
@@ -2467,7 +2467,7 @@ std::map<std::string, std::vector<std::string> > cpu::disassemble(const uint16_t
 	return out;
 }
 
-void cpu::step()
+bool cpu::step()
 {
 	it_is_a_trap = false;
 
@@ -2491,24 +2491,28 @@ void cpu::step()
 		add_register(7, 2);
 
 		if (double_operand_instructions(instr))
-			return;
+			return true;
 
 		if (conditional_branch_instructions(instr))
-			return;
+			return true;
 
 		if (condition_code_operations(instr))
-			return;
+			return true;
 
 		if (misc_operations(instr))
-			return;
+			return true;
 
 		DOLOG(warning, false, "UNHANDLED instruction %06o @ %06o", instr, instruction_start);
 
 		trap(010);  // floating point nog niet geimplementeerd
+
+		return false;
 	}
 	catch(const int exception_nr) {
 		TRACE("bus-trap during execution of command (%d)", exception_nr);
 	}
+
+	return true;
 }
 
 JsonDocument cpu::serialize()
diff --git a/cpu.h b/cpu.h
index f0db784..8f8ab34 100644
--- a/cpu.h
+++ b/cpu.h
@@ -141,7 +141,7 @@ public:
 
 	void reset();
 
-	void step();
+	bool step();
 
 	void pushStack(const uint16_t v);
 	uint16_t popStack();
diff --git a/main.cpp b/main.cpp
index 78b9260..2e6c301 100644
--- a/main.cpp
+++ b/main.cpp
@@ -136,14 +136,17 @@ int run_cpu_validation(console *const cnsl, const std::string & filename)
 				b->write_physical(element.first, element.second);
 		}
 
+		int cur_n_errors = 0;
+
 		// DO!
 		c->emulation_start();
 		disassemble(c, nullptr, c->getPC(), false);
-		c->step();
-
+		if (c->step() == false) {
+			cnsl->put_string_lf("Treated as an invalid instruction");
+			cur_n_errors++;
+		}
 		// VERIFY
-		int cur_n_errors = 0;
-		{
+		else {
 			auto after = test["after"];
 
 			cur_n_errors += !compare_values(cnsl, c->getPC(),  get_register_value(after, "PC" ), "PC" );