diff --git a/docs/tuning.md b/docs/tuning.md
index 1ed14091c054611e2ff1216a44cbd4dd12191f83..976f2eb8a7b23db8ae5b155e2dadc1956c17a6c2 100644
--- a/docs/tuning.md
+++ b/docs/tuning.md
@@ -115,7 +115,7 @@ Although there are two relevant configurations, the typical user should not need
 as the default values are applicable to most workloads:
 
 * `spark.memory.fraction` expresses the size of `M` as a fraction of the (JVM heap space - 300MB)
-(default 0.6). The rest of the space (25%) is reserved for user data structures, internal
+(default 0.6). The rest of the space (40%) is reserved for user data structures, internal
 metadata in Spark, and safeguarding against OOM errors in the case of sparse and unusually
 large records.
 * `spark.memory.storageFraction` expresses the size of `R` as a fraction of `M` (default 0.5).