diff --git a/src/prometheus/compiler/compiler.lua b/src/prometheus/compiler/compiler.lua
index acbbe39..eebb353 100644
--- a/src/prometheus/compiler/compiler.lua
+++ b/src/prometheus/compiler/compiler.lua
@@ -1969,19 +1969,30 @@ function Compiler:compileExpression(expression, funcDepth, numReturns)
                 retRegs[i] = self:allocRegister(false);
             end
         end
-        local argRegs = {};
-
+        
+        local regs = {};
+        local args = {};
         for i, expr in ipairs(expression.args) do
-            table.insert(argRegs, self:compileExpression(expr, funcDepth, 1)[1]);
+            if i == #expression.args and (expr.kind == AstKind.FunctionCallExpression or expr.kind == AstKind.PassSelfFunctionCallExpression or expr.kind == AstKind.VarargExpression) then
+                local reg = self:compileExpression(expr, funcDepth, self.RETURN_ALL)[1];
+                table.insert(args, Ast.FunctionCallExpression(
+                    self:unpack(scope),
+                    {self:register(scope, reg)}));
+                table.insert(regs, reg);
+            else
+                local reg = self:compileExpression(expr, funcDepth, 1)[1];
+                table.insert(args, self:register(scope, reg));
+                table.insert(regs, reg);
+            end
         end
 
         if(returnAll) then
-            self:addStatement(self:setRegister(scope, retRegs[1], Ast.TableConstructorExpression{Ast.TableEntry(Ast.FunctionCallExpression(self:register(scope, baseReg), self:registerList(scope, argRegs)))}), {retRegs[1]}, {baseReg, unpack(argRegs)}, true);
+            self:addStatement(self:setRegister(scope, retRegs[1], Ast.TableConstructorExpression{Ast.TableEntry(Ast.FunctionCallExpression(self:register(scope, baseReg), args))}), {retRegs[1]}, {baseReg, unpack(regs)}, true);
         else
             if(numReturns > 1) then
                 local tmpReg = self:allocRegister(false);
     
-                self:addStatement(self:setRegister(scope, tmpReg, Ast.TableConstructorExpression{Ast.TableEntry(Ast.FunctionCallExpression(self:register(scope, baseReg), self:registerList(scope, argRegs)))}), {tmpReg}, {baseReg, unpack(argRegs)}, true);
+                self:addStatement(self:setRegister(scope, tmpReg, Ast.TableConstructorExpression{Ast.TableEntry(Ast.FunctionCallExpression(self:register(scope, baseReg), args))}), {tmpReg}, {baseReg, unpack(regs)}, true);
     
                 for i, reg in ipairs(retRegs) do
                     self:addStatement(self:setRegister(scope, reg, Ast.IndexExpression(self:register(scope, tmpReg), Ast.NumberExpression(i))), {reg}, {tmpReg}, false);
@@ -1989,7 +2000,7 @@ function Compiler:compileExpression(expression, funcDepth, numReturns)
     
                 self:freeRegister(tmpReg, false);
             else
-                self:addStatement(self:setRegister(scope, retRegs[1], Ast.FunctionCallExpression(self:register(scope, baseReg), self:registerList(scope, argRegs))), {retRegs[1]}, {baseReg, unpack(argRegs)}, true);
+                self:addStatement(self:setRegister(scope, retRegs[1], Ast.FunctionCallExpression(self:register(scope, baseReg), args)), {retRegs[1]}, {baseReg, unpack(regs)}, true);
             end
         end
 
@@ -1997,7 +2008,7 @@ function Compiler:compileExpression(expression, funcDepth, numReturns)
         
 
         self:freeRegister(baseReg, false);
-        for i, reg in ipairs(argRegs) do
+        for i, reg in ipairs(regs) do
             self:freeRegister(reg, false);
         end