diff --git a/CHANGES.txt b/CHANGES.txt
index 6b6bc1f256..8877fa9f06 100644
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -1,4 +1,5 @@
 3.0.6
+ * Don't require HEAP_NEW_SIZE to be set when using G1 (CASSANDRA-11600)
  * Fix sstabledump not showing cells after tombstone marker (CASSANDRA-11654)
  * Ignore all LocalStrategy keyspaces for streaming and other related
    operations (CASSANDRA-11627)
diff --git a/conf/cassandra-env.ps1 b/conf/cassandra-env.ps1
index a322a4d2d2..794189f436 100644
--- a/conf/cassandra-env.ps1
+++ b/conf/cassandra-env.ps1
@@ -133,7 +133,7 @@ Function CalculateHeapSizes
         return
     }
 
-    if (($env:MAX_HEAP_SIZE -and !$env:HEAP_NEWSIZE) -or (!$env:MAX_HEAP_SIZE -and $env:HEAP_NEWSIZE))
+    if ((($env:MAX_HEAP_SIZE -and !$env:HEAP_NEWSIZE) -or (!$env:MAX_HEAP_SIZE -and $env:HEAP_NEWSIZE)) -and ($using_cms -eq $true))
     {
         echo "Please set or unset MAX_HEAP_SIZE and HEAP_NEWSIZE in pairs.  Aborting startup."
         exit 1
@@ -327,12 +327,6 @@ Function SetCassandraEnvironment
     # times. If in doubt, and if you do not particularly want to tweak, go
     # 100 MB per physical CPU core.
 
-    #$env:MAX_HEAP_SIZE="4096M"
-    #$env:HEAP_NEWSIZE="800M"
-    CalculateHeapSizes
-
-    ParseJVMInfo
-
     #GC log path has to be defined here since it needs to find CASSANDRA_HOME
     $env:JVM_OPTS="$env:JVM_OPTS -Xloggc:""$env:CASSANDRA_HOME/logs/gc.log"""
 
@@ -352,6 +346,12 @@ Function SetCassandraEnvironment
     $defined_xms = $env:JVM_OPTS -like '*Xms*'
     $using_cms = $env:JVM_OPTS -like '*UseConcMarkSweepGC*'
 
+    #$env:MAX_HEAP_SIZE="4096M"
+    #$env:HEAP_NEWSIZE="800M"
+    CalculateHeapSizes
+
+    ParseJVMInfo
+
     # We only set -Xms and -Xmx if they were not defined on jvm.options file
     # If defined, both Xmx and Xms should be defined together.
     if (($defined_xmx -eq $false) -and ($defined_xms -eq $false))
diff --git a/conf/cassandra-env.sh b/conf/cassandra-env.sh
index 83fe4c5443..0ba0c4e22e 100644
--- a/conf/cassandra-env.sh
+++ b/conf/cassandra-env.sh
@@ -121,41 +121,6 @@ case "$jvm" in
         ;;
 esac
 
-# Override these to set the amount of memory to allocate to the JVM at
-# start-up. For production use you may wish to adjust this for your
-# environment. MAX_HEAP_SIZE is the total amount of memory dedicated
-# to the Java heap. HEAP_NEWSIZE refers to the size of the young
-# generation. Both MAX_HEAP_SIZE and HEAP_NEWSIZE should be either set
-# or not (if you set one, set the other).
-#
-# The main trade-off for the young generation is that the larger it
-# is, the longer GC pause times will be. The shorter it is, the more
-# expensive GC will be (usually).
-#
-# The example HEAP_NEWSIZE assumes a modern 8-core+ machine for decent pause
-# times. If in doubt, and if you do not particularly want to tweak, go with
-# 100 MB per physical CPU core.
-
-#MAX_HEAP_SIZE="4G"
-#HEAP_NEWSIZE="800M"
-
-# Set this to control the amount of arenas per-thread in glibc
-#export MALLOC_ARENA_MAX=4
-
-# only calculate the size if it's not set manually
-if [ "x$MAX_HEAP_SIZE" = "x" ] && [ "x$HEAP_NEWSIZE" = "x" ]; then
-    calculate_heap_sizes
-else
-    if [ "x$MAX_HEAP_SIZE" = "x" ] ||  [ "x$HEAP_NEWSIZE" = "x" ]; then
-        echo "please set or unset MAX_HEAP_SIZE and HEAP_NEWSIZE in pairs (see cassandra-env.sh)"
-        exit 1
-    fi
-fi
-
-if [ "x$MALLOC_ARENA_MAX" = "x" ] ; then
-    export MALLOC_ARENA_MAX=4
-fi
-
 #GC log path has to be defined here because it needs to access CASSANDRA_HOME
 JVM_OPTS="$JVM_OPTS -Xloggc:${CASSANDRA_HOME}/logs/gc.log"
 
@@ -178,6 +143,41 @@ echo $JVM_OPTS | grep -q Xms
 DEFINED_XMS=$?
 echo $JVM_OPTS | grep -q UseConcMarkSweepGC
 USING_CMS=$?
+echo $JVM_OPTS | grep -q UseG1GC
+USING_G1=$?
+
+# Override these to set the amount of memory to allocate to the JVM at
+# start-up. For production use you may wish to adjust this for your
+# environment. MAX_HEAP_SIZE is the total amount of memory dedicated
+# to the Java heap. HEAP_NEWSIZE refers to the size of the young
+# generation. Both MAX_HEAP_SIZE and HEAP_NEWSIZE should be either set
+# or not (if you set one, set the other).
+#
+# The main trade-off for the young generation is that the larger it
+# is, the longer GC pause times will be. The shorter it is, the more
+# expensive GC will be (usually).
+#
+# The example HEAP_NEWSIZE assumes a modern 8-core+ machine for decent pause
+# times. If in doubt, and if you do not particularly want to tweak, go with
+# 100 MB per physical CPU core.
+
+#MAX_HEAP_SIZE="4G"
+#HEAP_NEWSIZE="800M"
+
+# Set this to control the amount of arenas per-thread in glibc
+#export MALLOC_ARENA_MAX=4
+
+# only calculate the size if it's not set manually
+if [ "x$MAX_HEAP_SIZE" = "x" ] && [ "x$HEAP_NEWSIZE" = "x" -o $USING_G1 -eq 0 ]; then
+    calculate_heap_sizes
+elif [ "x$MAX_HEAP_SIZE" = "x" ] ||  [ "x$HEAP_NEWSIZE" = "x" -a $USING_G1 -ne 0 ]; then
+    echo "please set or unset MAX_HEAP_SIZE and HEAP_NEWSIZE in pairs when using CMS GC (see cassandra-env.sh)"
+    exit 1
+fi
+
+if [ "x$MALLOC_ARENA_MAX" = "x" ] ; then
+    export MALLOC_ARENA_MAX=4
+fi
 
 # We only set -Xms and -Xmx if they were not defined on jvm.options file
 # If defined, both Xmx and Xms should be defined together.