diff --git a/components/compiler/exprparser.cpp b/components/compiler/exprparser.cpp
index 1268f602b..516879c40 100644
--- a/components/compiler/exprparser.cpp
+++ b/components/compiler/exprparser.cpp
@@ -9,6 +9,36 @@
 
 namespace Compiler
 {
+    char ExprParser::popUnaryOperator()
+    {
+        if (mOperators.empty())
+            return 0;
+    
+        char op = mOperators[mOperators.size()-1];
+        
+        if (op!='m') // unary -
+            return 0;
+            
+        mOperators.resize (mOperators.size()-1);
+            
+        return op;
+    }
+    
+    char ExprParser::popOperand (std::vector<Interpreter::Type_Code>& code)
+    {
+        Operand operand = mOperands[mOperands.size()-1];
+        mOperands.resize (mOperands.size()-1);
+    
+        if (operand.mType=='l')
+            Generator::pushInt (code, mLiterals, operand.mInteger);
+        else if (operand.mType=='f')
+            Generator::pushFloat (code, mLiterals, operand.mFloat);
+        else
+            throw std::logic_error ("unknown expression type");     
+            
+       return operand.mType;       
+    }
+
     ExprParser::ExprParser (ErrorHandler& errorHandler, Context& context, Locals& locals,
         Literals& literals)
     : Parser (errorHandler, context), mLocals (locals), mLiterals (literals),
@@ -18,7 +48,7 @@ namespace Compiler
     bool ExprParser::parseInt (int value, const TokenLoc& loc, Scanner& scanner)
     {
         if (mNextOperand)
-        {
+        {       
             Operand operand;
             operand.mType = 'l';
             operand.mInteger = value;
@@ -79,6 +109,17 @@ namespace Compiler
             return false;
         }
         
+        if (code==Scanner::S_minus)
+        {
+            if (mNextOperand)            
+            {
+                // unary
+                mOperators.push_back ('m');
+                mTokenLoc = loc;
+                return true;
+            }
+        }
+        
         return Parser::parseSpecial (code, loc, scanner);
     }
     
@@ -97,17 +138,24 @@ namespace Compiler
         if (mNextOperand)
             getErrorHandler().error ("syntax error in expression", mTokenLoc);
 
-        Operand operand = mOperands[mOperands.size()-1];
-        mOperands.clear();
-        
-        if (operand.mType=='l')
-            Generator::pushInt (code, mLiterals, operand.mInteger);
-        else if (operand.mType=='f')
-            Generator::pushFloat (code, mLiterals, operand.mFloat);
-        else
-            throw std::logic_error ("unknown expression type");
+        char type = ' ';
+
+        while (!mOperands.empty())
+        {
+            type = popOperand (code);
+                
+            while (char op = popUnaryOperator())
+            {
+                if (op=='m')
+                {
+                    Generator::negate (code, type);
+                }
+                else
+                    throw std::logic_error ("unknown unary operator");
+            }
+        }
         
-        return operand.mType;
+        return type;
     }    
 }
 
diff --git a/components/compiler/exprparser.hpp b/components/compiler/exprparser.hpp
index 0370e35e2..93f5db478 100644
--- a/components/compiler/exprparser.hpp
+++ b/components/compiler/exprparser.hpp
@@ -29,6 +29,11 @@ namespace Compiler
             bool mNextOperand;
             TokenLoc mTokenLoc;
             
+            char popUnaryOperator();
+            ///< returns 0 and not popping, if the next operator isn't unary
+            
+            char popOperand (std::vector<Interpreter::Type_Code>& code);
+            
         public:
     
             ExprParser (ErrorHandler& errorHandler, Context& context, Locals& locals,
diff --git a/components/compiler/generator.cpp b/components/compiler/generator.cpp
index 8d37f57a9..cf9f68eef 100644
--- a/components/compiler/generator.cpp
+++ b/components/compiler/generator.cpp
@@ -84,6 +84,16 @@ namespace
     {
         code.push_back (segment5 (2));
     }        
+
+    void opNegateInt (Compiler::Generator::CodeContainer& code)
+    {
+        code.push_back (segment5 (7));
+    }
+
+    void opNegateFloat (Compiler::Generator::CodeContainer& code)
+    {
+        code.push_back (segment5 (8));
+    }
 }
 
 namespace Compiler
@@ -145,6 +155,26 @@ namespace Compiler
                     assert (0);
             }
         }
+
+        void negate (CodeContainer& code, char valueType)
+        {
+            switch (valueType)
+            {
+                case 'l':
+                
+                    opNegateInt (code);
+                    break;
+                
+                case 'f':
+                
+                    opNegateFloat (code);
+                    break;
+                
+                default:
+                
+                    assert (0);
+            }
+        }
     }
 }
 
diff --git a/components/compiler/generator.hpp b/components/compiler/generator.hpp
index 061a30df4..42117eecb 100644
--- a/components/compiler/generator.hpp
+++ b/components/compiler/generator.hpp
@@ -19,6 +19,8 @@ namespace Compiler
 
         void assignToLocal (CodeContainer& code, char localType,
             int localIndex, const CodeContainer& value, char valueType);
+            
+        void negate (CodeContainer& code, char valueType);
     }
 }
 
diff --git a/components/interpreter/docs/vmformat.txt b/components/interpreter/docs/vmformat.txt
index ca76d00f3..1a4db8b56 100644
--- a/components/interpreter/docs/vmformat.txt
+++ b/components/interpreter/docs/vmformat.txt
@@ -58,6 +58,8 @@ op   3: convert stack[0] from integer to float
 op   4: replace stack[0] with integer literal index stack[0]
 op   5: replace stack[0] with float literal index stack[0]
 op   6: convert stack[0] from float to integer
-opcodes 7-33554431 unused
+op   7: invert sign of int value stack[0]
+op   8: invert sign of float value stack[0]
+opcodes 9-33554431 unused
 opcodes 33554432-67108863 reserved for extensions
 
diff --git a/components/interpreter/genericopcodes.hpp b/components/interpreter/genericopcodes.hpp
index 44e1e9cb4..db22ac089 100644
--- a/components/interpreter/genericopcodes.hpp
+++ b/components/interpreter/genericopcodes.hpp
@@ -39,6 +39,30 @@ namespace Interpreter
                 runtime[0] = *reinterpret_cast<Type_Data *> (&integerValue);
             }           
     };    
+    
+    class OpNegateInt : public Opcode0
+    {
+        public:
+        
+            virtual void execute (Runtime& runtime)
+            {
+                Type_Integer data = *reinterpret_cast<Type_Integer *> (&runtime[0]);
+                data = -data;
+                runtime[0] = *reinterpret_cast<Type_Data *> (&data);
+            }           
+    };    
+    
+    class OpNegateFloat : public Opcode0
+    {
+        public:
+        
+            virtual void execute (Runtime& runtime)
+            {
+                Type_Float data = *reinterpret_cast<Type_Float *> (&runtime[0]);
+                data = -data;
+                runtime[0] = *reinterpret_cast<Type_Data *> (&data);
+            }           
+    };    
 }
 
 #endif
diff --git a/components/interpreter/installopcodes.cpp b/components/interpreter/installopcodes.cpp
index df3f69201..15755a38a 100644
--- a/components/interpreter/installopcodes.cpp
+++ b/components/interpreter/installopcodes.cpp
@@ -13,7 +13,9 @@ namespace Interpreter
         interpreter.installSegment0 (0, new OpPushInt);
         interpreter.installSegment5 (3, new OpIntToFloat);
         interpreter.installSegment5 (6, new OpFloatToInt);
-    
+        interpreter.installSegment5 (7, new OpNegateInt);
+        interpreter.installSegment5 (8, new OpNegateFloat);
+            
         // local variables
         interpreter.installSegment5 (0, new OpStoreLocalShort);
         interpreter.installSegment5 (1, new OpStoreLocalLong);