diff --git a/src/compile.cpp b/src/compile.cpp
index 2217dd8689..4bb068af83 100644
--- a/src/compile.cpp
+++ b/src/compile.cpp
@@ -3491,24 +3491,27 @@ calculateJunctions(MyThread* t, Context* context, uintptr_t* originalRoots,
     case IpEvent: {
       ip = context->eventLog.get2(ei);
 
+      if (DebugFrameMaps) {
+        fprintf(stderr, "      roots at ip %3d: ", ip);
+        printSet(*roots);
+        fprintf(stderr, "\n");
+
+        fprintf(stderr, "      known at ip %3d: ", ip);
+        printSet(*known);
+        fprintf(stderr, "\n");
+      }
+
       if (context->visitTable[ip] > 1) {
         uintptr_t* tableRoots = context->rootTable + (ip * mapSize);
         uintptr_t* tableKnown = context->knownTable + (ip * mapSize);
         
-        if (DebugFrameMaps) {
-          fprintf(stderr, "      roots at ip %3d: ", ip);
-          printSet(*roots);
-          fprintf(stderr, "\n");
-
-          fprintf(stderr, "      known at ip %3d: ", ip);
-          printSet(*known);
-          fprintf(stderr, "\n");
-        }
-
         for (unsigned wi = 0; wi < mapSize; ++wi) {
           tableRoots[wi] &= ~(known[wi] & ~roots[wi]);
           tableRoots[wi] |= known[wi] & roots[wi] & ~tableKnown[wi];
           tableKnown[wi] |= known[wi];
+
+          roots[wi] = 0;
+          known[wi] = tableKnown[wi] & ~tableRoots[wi];
         }
 
         if (DebugFrameMaps) {
@@ -3520,9 +3523,6 @@ calculateJunctions(MyThread* t, Context* context, uintptr_t* originalRoots,
           printSet(*tableKnown);
           fprintf(stderr, "\n");
         }
-
-        memset(roots, 0, mapSize * BytesPerWord);
-        memset(known, 0, mapSize * BytesPerWord);
       }
 
       ei += 2;
@@ -3579,6 +3579,12 @@ updateTraceElements(MyThread* t, Context* context, uintptr_t* originalRoots,
     case IpEvent: {
       ip = context->eventLog.get2(ei);
 
+      if (DebugFrameMaps) {
+        fprintf(stderr, "        map at ip %3d: ", ip);
+        printSet(*roots);
+        fprintf(stderr, "\n");
+      }
+
       if (context->visitTable[ip] > 1) {
         uintptr_t* tableRoots = context->rootTable + (ip * mapSize);
         uintptr_t* tableKnown = context->knownTable + (ip * mapSize);
@@ -3609,12 +3615,6 @@ updateTraceElements(MyThread* t, Context* context, uintptr_t* originalRoots,
       TraceElement* te; context->eventLog.get(ei, &te, BytesPerWord);
       memcpy(te->map, roots, mapSize * BytesPerWord);
 
-      if (DebugFrameMaps) {
-        fprintf(stderr, "        map at ip %3d: ", ip);
-        printSet(*roots);
-        fprintf(stderr, "\n");
-      }
-
       ei += BytesPerWord;
     } break;
 
diff --git a/test/GC.java b/test/GC.java
index 196bd6c8cc..2b9b46fc8d 100644
--- a/test/GC.java
+++ b/test/GC.java
@@ -47,6 +47,16 @@ public class GC {
   }
 
   private static void stackMap3(boolean predicate) {
+    if (predicate) {
+      Object a = null;
+    } else {
+      int a = 42;
+    }
+
+    System.gc();
+  }
+
+  private static void stackMap4(boolean predicate) {
     int i = 2;
     if (predicate) {
       Object a = null;
@@ -61,6 +71,22 @@ public class GC {
     } while (i >= 0);
   }
 
+  private static void noop() { }
+
+  private static void stackMap5(boolean predicate) {
+    if (predicate) {
+      noop();
+    }
+
+    if (predicate) {
+      noop();
+    } else {
+      Object a = null;
+    }
+
+    System.gc();
+  }
+
   public static void main(String[] args) {
     Object[] array = new Object[1024 * 1024];
     array[0] = new Object();
@@ -87,6 +113,12 @@ public class GC {
 
     stackMap3(true);
     stackMap3(false);
+
+    stackMap4(true);
+    stackMap4(false);
+
+    stackMap5(true);
+    stackMap5(false);
   }
 
 }