diff --git a/src/init.cpp b/src/init.cpp
--- a/src/init.cpp
+++ b/src/init.cpp
@@ -789,7 +789,8 @@
         HelpMessageOpt("-blockprioritysize=<n>",
                        strprintf(_("Set maximum size of high-priority/low-fee "
                                    "transactions in bytes (default: %d)"),
-                                 DEFAULT_BLOCK_PRIORITY_SIZE));
+                                 DEFAULT_BLOCK_PRIORITY_SIZE_PER_MB *
+                                     DEFAULT_MAX_BLOCK_SIZE / ONE_MEGABYTE));
     strUsage += HelpMessageOpt(
         "-blockmintxfee=<amt>",
         strprintf(_("Set lowest fee rate (in %s/kB) for transactions to be "
diff --git a/src/miner.cpp b/src/miner.cpp
--- a/src/miner.cpp
+++ b/src/miner.cpp
@@ -562,7 +562,8 @@
     // How much of the block should be dedicated to high-priority transactions,
     // included regardless of the fees they pay.
     uint64_t nBlockPrioritySize =
-        GetArg("-blockprioritysize", DEFAULT_BLOCK_PRIORITY_SIZE);
+        GetArg("-blockprioritysize", DEFAULT_BLOCK_PRIORITY_SIZE_PER_MB *
+                                         DEFAULT_MAX_BLOCK_SIZE / ONE_MEGABYTE);
     nBlockPrioritySize = std::min(nMaxGeneratedBlockSize, nBlockPrioritySize);
     if (nBlockPrioritySize == 0) {
         return;
diff --git a/src/policy/policy.h b/src/policy/policy.h
--- a/src/policy/policy.h
+++ b/src/policy/policy.h
@@ -19,7 +19,7 @@
 static const uint64_t DEFAULT_MAX_GENERATED_BLOCK_SIZE = 2 * ONE_MEGABYTE;
 /** Default for -blockprioritysize, maximum space for zero/low-fee transactions
  * **/
-static const uint64_t DEFAULT_BLOCK_PRIORITY_SIZE = 0;
+static const uint64_t DEFAULT_BLOCK_PRIORITY_SIZE_PER_MB = 5000;
 /** Default for -blockmintxfee, which sets the minimum feerate for a transaction
  * in blocks created by mining code **/
 static const unsigned int DEFAULT_BLOCK_MIN_TX_FEE = 1000;
diff --git a/src/test/miner_tests.cpp b/src/test/miner_tests.cpp
--- a/src/test/miner_tests.cpp
+++ b/src/test/miner_tests.cpp
@@ -86,6 +86,9 @@
 
     GlobalConfig config;
 
+    // these 3 tests assume blockprioritysize is 0.
+    ForceSetArg("-blockprioritysize", "0");
+
     // Test that a medium fee transaction will be selected after a higher fee
     // rate package with a low fee rate parent.
     CMutableTransaction tx;