diff --git a/basicmath/ops/addition.py b/basicmath/ops/addition.py
index 3e78528..8054b20 100644
--- a/basicmath/ops/addition.py
+++ b/basicmath/ops/addition.py
@@ -5,6 +5,6 @@
 
 def add(a: Number, b: Number) -> Number:
     """Returns the sum of a & b."""
-    if (not isinstance(a, Number)) or (not isinstance(a, Number)):
+    if (not isinstance(a, Number)) or (not isinstance(b, Number)):
         raise TypeError
     return a + b
diff --git a/basicmath/ops/subtraction.py b/basicmath/ops/subtraction.py
index a2d603a..705f73b 100644
--- a/basicmath/ops/subtraction.py
+++ b/basicmath/ops/subtraction.py
@@ -5,6 +5,6 @@
 
 def subtract(a: Number, b: Number) -> Number:
     """Returns the difference of a & b."""
-    if (not isinstance(a, Number)) or (not isinstance(a, Number)):
+    if (not isinstance(a, Number)) or (not isinstance(b, Number)):
         raise TypeError
     return a - b