diff --git a/gklearn/kernels/graph_kernel.py b/gklearn/kernels/graph_kernel.py
index 90a0906..6d9517f 100644
--- a/gklearn/kernels/graph_kernel.py
+++ b/gklearn/kernels/graph_kernel.py
@@ -124,7 +124,13 @@ class GraphKernel(BaseEstimator): #, ABC):
 		self._is_transformed = True
 		if self.normalize:
 			X_diag, Y_diag = self.diagonals()
-			kernel_matrix /= np.sqrt(np.outer(Y_diag, X_diag))
+			old_settings = np.seterr(invalid='raise') # Catch FloatingPointError: invalid value encountered in sqrt.
+			try:
+				kernel_matrix /= np.sqrt(np.outer(Y_diag, X_diag))
+			except:
+				raise
+			finally:
+				np.seterr(**old_settings)
 
 		return kernel_matrix
 
@@ -150,9 +156,15 @@ class GraphKernel(BaseEstimator): #, ABC):
 		gram_matrix = self.compute_kernel_matrix()
 
 		# Normalize.
-		self._X_diag = np.diagonal(gram_matrix).copy()
 		if self.normalize:
-			gram_matrix /= np.sqrt(np.outer(self._X_diag, self._X_diag))
+			self._X_diag = np.diagonal(gram_matrix).copy()
+			old_settings = np.seterr(invalid='raise') # Catch FloatingPointError: invalid value encountered in sqrt.
+			try:
+				gram_matrix /= np.sqrt(np.outer(self._X_diag, self._X_diag))
+			except:
+				raise
+			finally:
+				np.seterr(**old_settings)
 
 		return gram_matrix