diff --git a/lib/valueflow.cpp b/lib/valueflow.cpp
index 89baf503cac..ecba13d38bc 100644
--- a/lib/valueflow.cpp
+++ b/lib/valueflow.cpp
@@ -6779,6 +6779,7 @@ static void valueFlowDynamicBufferSize(const TokenList& tokenlist, const SymbolD
         case Library::AllocFunc::BufferSize::strdup:
             if (arg1 && arg1->hasKnownValue()) {
                 const ValueFlow::Value& value = arg1->values().back();
+                assert(value.isKnown());
                 if (value.isTokValue() && value.tokvalue->tokType() == Token::eString)
                     sizeValue = Token::getStrLength(value.tokvalue) + 1; // Add one for the null terminator
             }
@@ -7037,7 +7038,10 @@ const ValueFlow::Value *ValueFlow::valueFlowConstantFoldAST(Token *expr, const S
         valueFlowConstantFoldAST(expr->astOperand2(), settings);
         valueFlowSetConstantValue(expr, settings);
     }
-    return expr && expr->hasKnownValue() ? &expr->values().front() : nullptr;
+    const auto* v = expr && expr->hasKnownValue() ? &expr->values().front() : nullptr;
+    if (v)
+        assert(v->isKnown());
+    return v;
 }
 
 struct ValueFlowState {
diff --git a/lib/vf_settokenvalue.cpp b/lib/vf_settokenvalue.cpp
index a04a9750c6b..3b4001c78b8 100644
--- a/lib/vf_settokenvalue.cpp
+++ b/lib/vf_settokenvalue.cpp
@@ -392,6 +392,7 @@ namespace ValueFlow
             // is condition always true/false?
             if (parent->astOperand1()->hasKnownValue()) {
                 const Value &condvalue = parent->astOperand1()->values().front();
+                assert(condvalue.isKnown());
                 const bool cond(condvalue.isTokValue() || (condvalue.isIntValue() && condvalue.intvalue != 0));
                 if (cond && !tok->astOperand1()) { // true condition, no second operator
                     setTokenValue(parent, condvalue, settings);