diff --git a/pymc/logprob/transforms.py b/pymc/logprob/transforms.py
index b4561e7cf7a..535b554e409 100644
--- a/pymc/logprob/transforms.py
+++ b/pymc/logprob/transforms.py
@@ -564,7 +564,7 @@ def measurable_special_exp_to_exp(fgraph, node):
     if isinstance(node.op.scalar_op, Exp2):
         return [pt.power(2, inp)]
     if isinstance(node.op.scalar_op, Expm1):
-        return [pt.exp(inp + 1)]
+        return [pt.exp(inp) - 1]
     if isinstance(node.op.scalar_op, Sigmoid):
         return [1 / (1 + pt.exp(-inp))]