diff --git a/gamecore/modules/world/actors/actor3D.lua b/gamecore/modules/world/actors/actor3D.lua
index 2ae451f..1cb4d3a 100644
--- a/gamecore/modules/world/actors/actor3D.lua
+++ b/gamecore/modules/world/actors/actor3D.lua
@@ -102,21 +102,21 @@ end
 -- All functions related to gravity
 
 function Actor3D:applyGravity(dt)
-  self.zsp = self.zsp - (self.grav * dt)
+  local grav = self.grav * -1
+  self.zsp = self.zsp + (grav * dt)
 
-  if utils.math.sign(self.zsp) == utils.math.sign(self.grav) then
+  if utils.math.sign(self.zsp) == utils.math.sign(grav) then
     self:checkGround( )
   end
 end
 
 function Actor3D:checkGround()
-  local dx, dy, dz = self.x, self.y, self.z + utils.math.sign(self.grav)
+  local dx, dy, dz = self.x, self.y, self.z - utils.math.sign(self.grav)
   local newx, newy, newz, cols, colNumber = self:checkCollision(dx, dy, dz)
-
   for i, col in ipairs(cols) do
     if (col.type == "touch") or (col.type == "bounce") or (col.type == "slide") then
       if not (self.grav == 0) then
-        if col.normal.z ~= utils.math.sign(self.grav) then self.onGround = true end
+        if col.normal.z == utils.math.sign(self.grav) then self.onGround = true end
       end
     end
   end