diff --git a/pkgs/applications/science/math/sage/sage-src.nix b/pkgs/applications/science/math/sage/sage-src.nix
index cd465a8c413a..4791d12450a9 100644
--- a/pkgs/applications/science/math/sage/sage-src.nix
+++ b/pkgs/applications/science/math/sage/sage-src.nix
@@ -29,6 +29,14 @@ stdenv.mkDerivation rec {
       url = "https://git.sagemath.org/sage.git/patch?id2=8bdc326ba57d1bb9664f63cf165a9e9920cc1afc&id=dc673c17555efca611f68398d5013b66e9825463";
       sha256 = "1hhannz7xzprijakn2w2d0rhd5zv2zikik9p51i87bas3nc658f7";
     })
+    
+    # `is_unitary` test in `matrix_double_dense.pyx` fails with some BLAS implementations
+    # https://trac.sagemath.org/ticket/29297 should be included in 9.1
+    (fetchpatch {
+      name = "is_unitary-special-case.patch";
+      url = "https://git.sagemath.org/sage.git/patch?id=cc3eb9ffa991e328b09028d32aab7e7cc2ddbb6a";
+      sha256 = "0jq4w8hnp5c9q99011ldr4n3knvm1rx2g85z0hidv3i9x868p0ay";
+    })
 
     # Unfortunately inclusion in upstream sage was rejected. Instead the bug was
     # fixed in python, but of course not backported to 2.7. So we'll probably