diff --git a/brainpy/_src/dyn/synapses/abstract_models.py b/brainpy/_src/dyn/synapses/abstract_models.py
index 3e8b23d2..2125da34 100644
--- a/brainpy/_src/dyn/synapses/abstract_models.py
+++ b/brainpy/_src/dyn/synapses/abstract_models.py
@@ -494,7 +494,7 @@ class Alpha(SynDyn):
   .. math::
 
       \begin{aligned}
-      &\tau \frac{d g}{d t}=-\frac{g}{\tau}+h \\
+      &\frac{d g}{d t}=-\frac{g}{\tau}+\frac{h}{\tau} \\
       &\frac{d h}{d t}=-\frac{h}{\tau}+\delta\left(t_{0}-t\right)
       \end{aligned}
 
diff --git a/brainpy/_src/dynold/synapses/abstract_models.py b/brainpy/_src/dynold/synapses/abstract_models.py
index aecd8ab2..f345050c 100644
--- a/brainpy/_src/dynold/synapses/abstract_models.py
+++ b/brainpy/_src/dynold/synapses/abstract_models.py
@@ -516,7 +516,7 @@ class Alpha(_TwoEndConnAlignPre):
 
       \begin{aligned}
       &g_{\mathrm{syn}}(t)= g_{\mathrm{max}} g \\
-      &\frac{d g}{d t}=-\frac{g}{\tau}+h \\
+      &\frac{d g}{d t}=-\frac{g}{\tau}+\frac{h}{\tau} \\
       &\frac{d h}{d t}=-\frac{h}{\tau}+\delta\left(t_{0}-t\right)
       \end{aligned}