diff --git a/source/m3_code.c b/source/m3_code.c
index a5dd5d3..b399b82 100644
--- a/source/m3_code.c
+++ b/source/m3_code.c
@@ -5,6 +5,7 @@
 //  Copyright © 2019 Steven Massey. All rights reserved.
 //
 
+#include <limits.h>
 #include "m3_code.h"
 #include "m3_env.h"
 
@@ -15,9 +16,23 @@ IM3CodePage  NewCodePage  (IM3Runtime i_runtime, u32 i_minNumLines)
 {
     IM3CodePage page;
 
+    // check multiplication overflow
+    if (i_minNumLines > UINT_MAX / sizeof (code_t)) {
+        return NULL;
+    }
     u32 pageSize = sizeof (M3CodePageHeader) + sizeof (code_t) * i_minNumLines;
 
+    // check addition overflow
+    if (pageSize < sizeof (M3CodePageHeader)) {
+        return NULL;
+    }
+
     pageSize = (pageSize + (d_m3CodePageAlignSize-1)) & ~(d_m3CodePageAlignSize-1); // align
+    // check alignment overflow
+    if (pageSize == 0) {
+        return NULL;
+    }
+
     page = (IM3CodePage)m3_Malloc ("M3CodePage", pageSize);
 
     if (page)
diff --git a/source/m3_compile.c b/source/m3_compile.c
index 2baf069..3fa533a 100644
--- a/source/m3_compile.c
+++ b/source/m3_compile.c
@@ -322,11 +322,8 @@ u16  GetExtraSlotForStackIndex  (IM3Compilation o, u16 i_stackIndex)
 static inline
 void  TouchSlot  (IM3Compilation o, u16 i_slot)
 {
-    if (o->function)
-    {
-        // op_Entry uses this value to track and detect stack overflow
-        o->maxStackSlots = M3_MAX (o->maxStackSlots, i_slot + 1);
-    }
+    // op_Entry uses this value to track and detect stack overflow
+    o->maxStackSlots = M3_MAX (o->maxStackSlots, i_slot + 1);
 }
 
 static inline
@@ -1900,6 +1897,7 @@ _   (CompileBlock (o, blockType, i_opcode));
 static
 M3Result  CompileElseBlock  (IM3Compilation o, pc_t * o_startPC, IM3FuncType i_blockType)
 {
+    IM3CodePage savedPage = o->page;
 _try {
 
     IM3CodePage elsePage;
@@ -1907,19 +1905,17 @@ _   (AcquireCompilationCodePage (o, & elsePage));
 
     * o_startPC = GetPagePC (elsePage);
 
-    IM3CodePage savedPage = o->page;
     o->page = elsePage;
 
 _   (CompileBlock (o, i_blockType, c_waOp_else));
 
 _   (EmitOp (o, op_Branch));
     EmitPointer (o, GetPagePC (savedPage));
-
-    ReleaseCompilationCodePage (o);
-
-    o->page = savedPage;
-
 } _catch:
+    if(o->page != savedPage) {
+        ReleaseCompilationCodePage (o);
+    }
+    o->page = savedPage;
     return result;
 }
 
@@ -2702,7 +2698,13 @@ _try {
 _           (PopType (o, type));
         }
     }
-    else o->stackIndex -= numParams;
+    else {
+        if (IsStackPolymorphic (o) && o->block.blockStackIndex + numParams > o->stackIndex) {
+            o->stackIndex = o->block.blockStackIndex;
+        } else {
+            o->stackIndex -= numParams;
+        }
+    }
 
     u16 paramIndex = o->stackIndex;
     block->exitStackIndex = paramIndex; // consume the params at block exit
@@ -2730,7 +2732,7 @@ _           (PopType (o, type));
         u16 slot = GetSlotForStackIndex (o, paramIndex + i);
         Push (o, type, slot);
 
-        if (slot >= o->slotFirstDynamicIndex)
+        if (slot >= o->slotFirstDynamicIndex && slot != c_slotUnused)
             MarkSlotsAllocatedByType (o, slot, type);
     }