--- a/memory/build/mozjemalloc.cpp
+++ b/memory/build/mozjemalloc.cpp
@@ -382,20 +382,23 @@ void *_mmap(void *addr, size_t length, i
 #define	RUN_MAX_OVRHD		0x0000003dU
 #define	RUN_MAX_OVRHD_RELAX	0x00001800U
 
 /*
  * When MALLOC_STATIC_PAGESIZE is defined, the page size is fixed at
  * compile-time for better performance, as opposed to determined at
  * runtime. Some platforms can have different page sizes at runtime
  * depending on kernel configuration, so they are opted out by default.
+ * Debug builds are opted out too, for test coverage.
  */
+#ifndef MOZ_DEBUG
 #if !defined(__ia64__) && !defined(__sparc__) && !defined(__mips__) && !defined(__aarch64__)
 #define MALLOC_STATIC_PAGESIZE 1
 #endif
+#endif
 
 /* Various quantum-related settings. */
 
 #define QUANTUM_DEFAULT  (size_t(1) << QUANTUM_2POW_MIN)
 static const size_t quantum = QUANTUM_DEFAULT;
 static const size_t quantum_mask = QUANTUM_DEFAULT - 1;
 
 /* Various bin-related settings. */