diff --git a/ffcv/memory_allocator.py b/ffcv/memory_allocator.py
index c869f684..6faf55a6 100644
--- a/ffcv/memory_allocator.py
+++ b/ffcv/memory_allocator.py
@@ -37,7 +37,7 @@ def malloc(self, size):
         # print(f"Allocating {size} bytes")
         if size > self.page_size:
             raise ValueError(f"Tried allocating {size} but" +
-                             " page size is {self.page_size}")
+                             f" page size is {self.page_size}")
 
         if size > self.space_left_in_page:
             self.flush_page()