diff --git a/src/CBot/CBotInstr/CBotExprUnaire.cpp b/src/CBot/CBotInstr/CBotExprUnaire.cpp
index 0080a468..e4d1ec3f 100644
--- a/src/CBot/CBotInstr/CBotExprUnaire.cpp
+++ b/src/CBot/CBotInstr/CBotExprUnaire.cpp
@@ -41,7 +41,7 @@ CBotExprUnaire::~CBotExprUnaire()
 }
 
 ////////////////////////////////////////////////////////////////////////////////
-CBotInstr* CBotExprUnaire::Compile(CBotToken* &p, CBotCStack* pStack)
+CBotInstr* CBotExprUnaire::Compile(CBotToken* &p, CBotCStack* pStack, bool bLiteral)
 {
     int op = p->GetType();
     CBotToken*    pp = p;
@@ -52,7 +52,10 @@ CBotInstr* CBotExprUnaire::Compile(CBotToken* &p, CBotCStack* pStack)
     CBotExprUnaire* inst = new CBotExprUnaire();
     inst->SetToken(pp);
 
-    if (nullptr != (inst->m_expr = CBotParExpr::Compile(p, pStk )))
+    if (!bLiteral) inst->m_expr = CBotParExpr::Compile(p, pStk);
+    else inst->m_expr = CBotParExpr::CompileLitExpr(p, pStk);
+
+    if (inst->m_expr != nullptr)
     {
         if (op == ID_ADD && pStk->GetType() < CBotTypBoolean)        // only with the number
             return pStack->Return(inst, pStk);
diff --git a/src/CBot/CBotInstr/CBotExprUnaire.h b/src/CBot/CBotInstr/CBotExprUnaire.h
index e7e58c74..b15d2552 100644
--- a/src/CBot/CBotInstr/CBotExprUnaire.h
+++ b/src/CBot/CBotInstr/CBotExprUnaire.h
@@ -34,12 +34,13 @@ public:
     ~CBotExprUnaire();
 
     /*!
-     * \brief Compile
-     * \param p
-     * \param pStack
-     * \return
+     * \brief Compile an expression with a unary operator
+     * \param p[in, out] Pointer to first token of the expression, will be updated to point to first token after the expression
+     * \param pStack Current compilation stack frame
+     * \param bLiteral If true, compiles only literal expressions Ex: ~11, -4.0, !false, not true
+     * \return The compiled instruction or nullptr
      */
-    static CBotInstr* Compile(CBotToken* &p, CBotCStack* pStack);
+    static CBotInstr* Compile(CBotToken* &p, CBotCStack* pStack, bool bLiteral = false);
 
     /*!
      * \brief Execute
diff --git a/src/CBot/CBotInstr/CBotParExpr.cpp b/src/CBot/CBotInstr/CBotParExpr.cpp
index b0c2f1c1..0a608c32 100644
--- a/src/CBot/CBotInstr/CBotParExpr.cpp
+++ b/src/CBot/CBotInstr/CBotParExpr.cpp
@@ -132,7 +132,7 @@ CBotInstr* CBotParExpr::Compile(CBotToken* &p, CBotCStack* pStack)
         return pStack->Return(nullptr, pStk);
     }
 
-    return CompileLitExpr(p, pStack);
+    return CBotParExpr::CompileLitExpr(p, pStack);
 }
 
 ////////////////////////////////////////////////////////////////////////////////
@@ -142,6 +142,11 @@ CBotInstr* CBotParExpr::CompileLitExpr(CBotToken* &p, CBotCStack* pStack)
 
     CBotToken* pp = p;
 
+    // is this a unary operation?
+    CBotInstr* inst = CBotExprUnaire::Compile(p, pStk, true);
+    if (inst != nullptr || !pStk->IsOk())
+        return pStack->Return(inst, pStk);
+
     // is it a number or DefineNum?
     if (p->GetType() == TokenTypNum ||
         p->GetType() == TokenTypDef )
diff --git a/test/unit/CBot/CBot_test.cpp b/test/unit/CBot/CBot_test.cpp
index 2f8bb503..5d3b72c3 100644
--- a/test/unit/CBot/CBot_test.cpp
+++ b/test/unit/CBot/CBot_test.cpp
@@ -2385,4 +2385,20 @@ TEST_F(CBotUT, ParametersWithDefaultValues)
         "\n",
         CBotErrAmbiguousCall
     );
+
+    ExecuteTest(
+        "extern void DefaultValueUnaryExpression() {\n"
+        "    TestNumbers();\n"
+        "    TestBool();\n"
+        "}\n"
+        "void TestNumbers(int i = -1, float f = -1, int ii = ~1) {\n"
+        "    ASSERT(i == -1);\n"
+        "    ASSERT(f == -1.0);\n"
+        "    ASSERT(ii == ~1);\n"
+        "}\n"
+        "void TestBool(bool b = !false, bool b2 = not false) {\n"
+        "    ASSERT(true == b);\n"
+        "    ASSERT(true == b2);\n"
+        "}\n"
+    );
 }