diff --git a/src/nimkalc/objects/ast.nim b/src/nimkalc/objects/ast.nim
index 86ec55f..e1f2760 100644
--- a/src/nimkalc/objects/ast.nim
+++ b/src/nimkalc/objects/ast.nim
@@ -100,6 +100,16 @@ template ensureNonZero(node: AstNode) =
           raise newException(CatchableError, &"invalid node kind '{node.kind}' for ensureNonZero")
 
 
+template ensurePositive(node: AstNode) =
+  ## Handy template to ensure that a given node's value is positive
+  if node.value < 0.0:
+      case node.kind:
+        of NodeKind.Float, NodeKind.Integer:
+            raise newException(MathError, "value must be positive")
+        else:
+          raise newException(CatchableError, &"invalid node kind '{node.kind}' for ensureNonZero")
+
+
 template ensureIntegers(left, right: AstNode) =
   ## Ensures both operands are integers
   if left.kind != NodeKind.Integer or right.kind != NodeKind.Integer:
@@ -159,6 +169,7 @@ proc visit_call(self: NodeVisitor, node: AstNode): AstNode =
     of "tan":
       callFunction(tan, self.eval(node.arguments[0]).value)
     of "sqrt":
+      ensurePositive(arg)
       callFunction(sqrt, self.eval(node.arguments[0]).value)
     of "log":
       let arg = self.eval(node.arguments[0])
@@ -222,8 +233,8 @@ proc visit_binary(self: NodeVisitor, node: AstNode): AstNode =
       result = handleBinary(left, right, `/`)
     of TokenType.Modulo:
       # Modulo is a bit special since we must have integers
-      ensureNonZero(right)
       ensureIntegers(left, right)
+      ensureNonZero(right)
       result = AstNode(kind: NodeKind.Integer, value: float(int(left.value) mod int(right.value)))
     of TokenType.Exp:
       result = handleBinary(left, right, pow)
@@ -245,5 +256,7 @@ proc visit_unary(self: NodeVisitor, node: AstNode): AstNode =
           result = AstNode(kind: NodeKind.Integer, value: -expr.value)
         else:
           discard  # Unreachable
+    of TokenType.Plus:
+        result = node  # Unary + does nothing
     else:
       discard  # Unreachable