diff --git a/docs/commands/simgenotype.rst b/docs/commands/simgenotype.rst
index 67c5960b..53452fb0 100644
--- a/docs/commands/simgenotype.rst
+++ b/docs/commands/simgenotype.rst
@@ -75,8 +75,9 @@ If speed is important, it's generally faster to use PGEN files than VCFs.
   --pop_field \
   --out tests/data/example_simgenotype.pgen
 
-Writing PGEN files will require more memory than writing VCFs. The memory required will depend on the number of simulated samples and variants.
-You can reduce the memory required by this step by writing the variants in chunks. Just specify a ``--chunk-size`` value.
+.. warning::
+  Writing PGEN files will require more memory than writing VCFs. The memory required will depend on the number of simulated samples and variants.
+  You can reduce the memory required by this step by writing the variants in chunks. Just specify a ``--chunk-size`` value.
 
 All files used in these examples are described :doc:`here </project_info/example_files>`.