diff --git a/errors.lua b/errors.lua
index 57e0702..26ae176 100644
--- a/errors.lua
+++ b/errors.lua
@@ -145,7 +145,7 @@ return function (module_name)
         return setmetatable(args[1] or {}, {
             __index = function (t, k)
                 local keys = {}
-                for k in pairs(t) do  keys[#keys+1] = k  end
+                for k in pairs(t) do  keys[#keys+1] = tostring(k)  end
                 if #keys == 0 then  external_error(err_hdl, '', 'Attempting to index unknown key %s in an empty table.', k)  end
                 correct_error(err_hdl, '', 'Attempting to index unknown key %s, maybe you meant %s?', k, keys)
             end
diff --git a/string_distance.lua b/string_distance.lua
index f9a90ea..f0bd122 100644
--- a/string_distance.lua
+++ b/string_distance.lua
@@ -42,9 +42,8 @@ local function levenshtein (str1, str2)
     -- Adapted from the C version given at: https://en.wikibooks.org/wiki/Algorithm_Implementation/Strings/Levenshtein_distance
 
     -- Error handeling.
-    assert(type(str1) == 'string')
-    assert(type(str2) == 'string')
-
+    if type(str1) ~= 'string' then  error(('[errors/internal]: Bad argument #1 to levenshtein, expected string, got %s (%s)'):format(str1, type(str1)))  end
+    if type(str2) ~= 'string' then  error(('[errors/internal]: Bad argument #1 to levenshtein, expected string, got %s (%s)'):format(str2, type(str2)))  end
 
     -- Do work
     local str1, str2 = str1:lower(), str2:lower()
@@ -90,8 +89,8 @@ local function longest_common_subsequence (str1, str2)
     -- Higher numbers denote more similar strings.
 
     -- Error handeling.
-    assert(type(str1) == 'string')
-    assert(type(str2) == 'string')
+    if type(str1) ~= 'string' then  error(('[errors/internal]: Bad argument #1 to longest_common_subsequence, expected string, got %s (%s)'):format(str1, type(str1)))  end
+    if type(str2) ~= 'string' then  error(('[errors/internal]: Bad argument #1 to longest_common_subsequence, expected string, got %s (%s)'):format(str2, type(str2)))  end
 
     -- Do work
     local str1, str2 = str1:lower(), str2:lower()
@@ -178,7 +177,7 @@ local function strings_with_highest_similarity (str, list_of_other_str)
     if type(str) ~= 'string' then  error(('[errors/internal]: Bad argument #1, expected string, got %s (%s)'):format(str, type(str))) end
     if type(list_of_other_str) ~= 'table'  then  error(('[errors/internal]: Bad argument #2, expected table, got %s (%s)'):format(list_of_other_str, type(list_of_other_str))) end
     for i = 1, #list_of_other_str do
-        if type(list_of_other_str[i]) ~= 'string'  then  error(('[errors/internal]: Bad argument #2, expected sequence of strings, but got %s (%s) on index %i'):format(list_of_other_str[i], type(list_of_other_str[i])), i) end
+        if type(list_of_other_str[i]) ~= 'string'  then  error(('[errors/internal]: Bad argument #2, expected sequence of strings, but got %s (%s) on index %i'):format(list_of_other_str[i], type(list_of_other_str[i]), i)) end
     end
 
     -- Do work
diff --git a/test/test_errors.lua b/test/test_errors.lua
index 69a508a..eb866a2 100644
--- a/test/test_errors.lua
+++ b/test/test_errors.lua
@@ -97,14 +97,27 @@ end)
 
 SUITE:addTest('Strict tables can be accessed normally', function()
 	local t   =  error.strict_table { a = 1, b = 2, c = 3 }
-	assert(t.a, 1)
-	assert(t.b, 2)
-	assert(t.c, 3)
+	assert_equal(t.a, 1)
+	assert_equal(t.b, 2)
+	assert_equal(t.c, 3)
+end)
+
+SUITE:addTest('Strict tables with number keys works as well', function()
+	local t   =  error.strict_table { 'hi', 'hello', 'world' }
+	assert_equal(t[1], 'hi')
+	assert_equal(t[2], 'hello')
+	assert_equal(t[3], 'world')
 end)
 
 SUITE:addTest('Strict tables throw errors on unknown indices', function()
 	local t   =  error.strict_table { a = 1, b = 2, c = 3 }
-	bad_call(function() return t.hello end)
+	print(bad_call(function() return t.hello end))
+end)
+
+SUITE:addTest('Strict tables throw errors on unknown indices, even if table contains number keys', function()
+	local t   =  error.strict_table { 'hi', 'hello', 'world' }
+	local msg = bad_call(function() return t.hello end)
+	assert_equal('[test_errors]: Attempting to index unknown key hello, maybe you meant 1, 2 or 3?', msg)
 end)
 
 SUITE:addTest('Strict tables throw specific error on empty table', function()
diff --git a/test/test_string_distance.lua b/test/test_string_distance.lua
index 64645d4..14aad81 100644
--- a/test/test_string_distance.lua
+++ b/test/test_string_distance.lua
@@ -115,6 +115,15 @@ SUITE:addTest('strings_with_highest_similarity example 1', function()
 	assert_equal( 'Allan Turing', output[1] )
 end)
 
+SUITE:addTest('strings_with_highest_similarity not defined on non-strings', function()
+	local strings = { 'Ada Lovelace', 'Charles Babbage ', 'Allan Turing', 'Grace Hopper' }
+	bad_call(strings_with_highest_similarity, 132, strings)
+	local strings = { 'Ada Lovelace', 'Charles Babbage ', 'Allan Turing', 4, 'Grace Hopper' }
+	bad_call(strings_with_highest_similarity, 'turning', strings)
+	local strings = { 'Ada Lovelace', 'Charles Babbage ', 'Allan Turing', {}, 'Grace Hopper' }
+	bad_call(strings_with_highest_similarity, 'turning', strings)
+end)
+
 --------------------------------------------------------------------------------