diff --git a/src/lol/base/array.h b/src/lol/base/array.h
index 9c17f415..33996097 100644
--- a/src/lol/base/array.h
+++ b/src/lol/base/array.h
@@ -18,6 +18,8 @@
 #if !defined __LOL_BASE_ARRAY_H__
 #define __LOL_BASE_ARRAY_H__
 
+#include <lol/base/assert.h>
+
 #include <new>
 #include <stdint.h>
 
@@ -118,21 +120,29 @@ public:
 
     inline Element& operator[](int n)
     {
+        /* Allow array[0] even if size is zero so that people can
+         * always use &array[0] to get a pointer to the data. */
+        ASSERT(n >= 0);
+        ASSERT(n < m_count || (!n && !m_count));
         return m_data[n];
     }
 
     inline Element const& operator[](int n) const
     {
+        ASSERT(n >= 0);
+        ASSERT(n < m_count || (!n && !m_count));
         return m_data[n];
     }
 
     inline Element& Last()
     {
+        ASSERT(m_count > 0);
         return m_data[m_count - 1];
     }
 
     inline Element const& Last() const
     {
+        ASSERT(m_count > 0);
         return m_data[m_count - 1];
     }
 
@@ -158,11 +168,14 @@ public:
 
     inline void Pop()
     {
+        ASSERT(m_count > 0);
         Remove(m_count - 1, 1);
     }
 
     void Remove(int pos, int todelete = 1)
     {
+        ASSERT(pos >= 0);
+        ASSERT(pos + todelete <= m_count);
         for (int i = pos; i + todelete < m_count; i++)
             m_data[i] = m_data[i + todelete];
         for (int i = m_count - todelete; i < m_count; i++)
@@ -172,6 +185,7 @@ public:
 
     void Resize(int count, Element e = Element())
     {
+        ASSERT(count > 0);
         Reserve(count);
 
         /* Too many elements? Remove them. */
diff --git a/src/lol/base/string.h b/src/lol/base/string.h
index 6b15d0c8..1ecbfe88 100644
--- a/src/lol/base/string.h
+++ b/src/lol/base/string.h
@@ -17,6 +17,7 @@
 #if !defined __LOL_BASE_STRING_H__
 #define __LOL_BASE_STRING_H__
 
+#include <lol/base/assert.h>
 #include <lol/base/array.h>
 
 #include <cstring>
@@ -41,6 +42,7 @@ public:
       : Super()
     {
         using namespace std;
+        ASSERT(str);
         Resize((int)strlen(str));
         memcpy(&(*this)[0], str, Count() + 1);
     }
@@ -49,9 +51,10 @@ public:
       : Super()
     {
         using namespace std;
+        ASSERT(str);
         Resize(count);
         memcpy(&(*this)[0], str, count);
-        (*this)[count] = '\0';
+        ((Super &)*this)[count] = '\0';
     }
 
     inline String(String const &s)
@@ -61,21 +64,27 @@ public:
 
     inline char &operator [](int n)
     {
+        ASSERT(n >= 0);
+        ASSERT(n < Count() || (!n && !Count()));
         return ((Super &)*this)[n];
     }
 
     inline char const &operator [](int n) const
     {
+        ASSERT(n >= 0);
+        ASSERT(n < Count() || (!n && !Count()));
         return ((Super const &)*this)[n];
     }
 
     inline char &Last()
     {
+        ASSERT(Count() > 0);
         return (*this)[Count() - 1];
     }
 
     inline char const &Last() const
     {
+        ASSERT(Count() > 0);
         return (*this)[Count() - 1];
     }
 
@@ -86,6 +95,7 @@ public:
 
     void Resize(int count)
     {
+        ASSERT(count >= 0, "count = %d", count);
         ((Super &)*this).Resize(count + 1);
         ((Super &)*this).Last() = '\0';
     }