diff --git a/ext/c4core b/ext/c4core
index 0a21dfc8c..cb4d74334 160000
--- a/ext/c4core
+++ b/ext/c4core
@@ -1 +1 @@
-Subproject commit 0a21dfc8cdc7521e9576f117529adbb59c466f74
+Subproject commit cb4d74334c4609d08064fcce0a1ff06ff088cf4e
diff --git a/src/c4/yml/parse.cpp b/src/c4/yml/parse.cpp
index 4a7484138..65e3bd706 100644
--- a/src/c4/yml/parse.cpp
+++ b/src/c4/yml/parse.cpp
@@ -5084,7 +5084,7 @@ FilterResult Parser::filter_scalar_dquoted_in_place(substr dst, size_t cap)
 //-----------------------------------------------------------------------------
 // block filtering helpers
 
-inline size_t _find_last_newline_and_larger_indentation(csubstr s, size_t indentation) noexcept
+size_t _find_last_newline_and_larger_indentation(csubstr s, size_t indentation) noexcept
 {
     if(indentation + 1 > s.len)
         return npos;
@@ -5099,12 +5099,6 @@ inline size_t _find_last_newline_and_larger_indentation(csubstr s, size_t indent
                 return i;
         }
     }
-    //_RYML_CB_ASSERT(this->callbacks(), _find_last_newline_and_larger_indentation("ab\n\n\n", 0) == npos);
-    //_RYML_CB_ASSERT(this->callbacks(), _find_last_newline_and_larger_indentation("ab\n \n\n", 0) == 2);
-    //_RYML_CB_ASSERT(this->callbacks(), _find_last_newline_and_larger_indentation("ab\n\n \n", 0) == 3);
-    //_RYML_CB_ASSERT(this->callbacks(), _find_last_newline_and_larger_indentation("ab\n \n \n", 0) == 4);
-    //_RYML_CB_ASSERT(this->callbacks(), _find_last_newline_and_larger_indentation("ab\n \n  \n", 1) == 4);
-    //_RYML_CB_ASSERT(this->callbacks(), _find_last_newline_and_larger_indentation("ab\n  \n \n", 1) == 2);
     return npos;
 }
 
@@ -5516,7 +5510,6 @@ void Parser::_filter_block_folded_newlines(FilterProcessor &C4_RESTRICT proc, si
         case '\t':
             {
                 size_t first = proc.rem().first_not_of(" \t");
-                //size_t first = proc.rem().first_not_of(' ');
                 _c4dbgfbf("space. first={}", first);
                 if(first == npos)
                     first = proc.rem().len;
@@ -5549,7 +5542,6 @@ void Parser::_filter_block_folded_newlines(FilterProcessor &C4_RESTRICT proc, si
 template<class FilterProcessor>
 void Parser::_filter_block_folded_indented_block(FilterProcessor &C4_RESTRICT proc, size_t indentation, size_t len, size_t curr_indentation) noexcept
 {
-    //_RYML_CB_ASSERT(this->callbacks(), proc.rem().first_not_of(' ') == curr_indentation);
     _RYML_CB_ASSERT(this->callbacks(), (proc.rem().first_not_of(" \t") == curr_indentation) || (proc.rem().first_not_of(" \t") == npos));
     proc.copy(curr_indentation);
     while(proc.has_more_chars(len))
diff --git a/test/test_filter.cpp b/test/test_filter.cpp
index 2d45edcd6..7d2b945e8 100644
--- a/test/test_filter.cpp
+++ b/test/test_filter.cpp
@@ -914,6 +914,17 @@ TEST(FilterProcessorSrcDst, translate_esc_bulk_excess)
     EXPECT_EQ(t.dst, "aaabbbcccddd^^");
 }
 
+TEST(Filter, _find_last_newline_and_larger_indentation)
+{
+    size_t _find_last_newline_and_larger_indentation(csubstr s, size_t indentation) noexcept;
+    EXPECT_EQ(_find_last_newline_and_larger_indentation("ab\n\n\n", 0), npos);
+    EXPECT_EQ(_find_last_newline_and_larger_indentation("ab\n \n\n", 0), 2u);
+    EXPECT_EQ(_find_last_newline_and_larger_indentation("ab\n\n \n", 0), 3u);
+    EXPECT_EQ(_find_last_newline_and_larger_indentation("ab\n \n \n", 0), 4u);
+    EXPECT_EQ(_find_last_newline_and_larger_indentation("ab\n \n  \n", 1), 4u);
+    EXPECT_EQ(_find_last_newline_and_larger_indentation("ab\n  \n \n", 1), 2u);
+}
+
 } // namespace yml
 } // namespace c4
 
diff --git a/test/test_number.cpp b/test/test_number.cpp
index 44676404b..a9344becf 100644
--- a/test/test_number.cpp
+++ b/test/test_number.cpp
@@ -1,4 +1,9 @@
 #include "./test_group.hpp"
+#ifdef RYML_SINGLE_HEADER
+#include <ryml_all.hpp>
+#else
+#include <c4/charconv.hpp>
+#endif
 
 namespace c4 {
 namespace yml {
diff --git a/tools/amalgamate.py b/tools/amalgamate.py
index ccc272e17..d17e2208f 100644
--- a/tools/amalgamate.py
+++ b/tools/amalgamate.py
@@ -38,7 +38,19 @@
 #include <stdarg.h>
 """
 
-ryml_preamble = f"""
+
+def amalgamate_ryml(filename: str,
+                    with_c4core: bool,
+                    with_fastfloat: bool,
+                    with_stl: bool):
+    c4core_amalgamated = ""
+    if with_c4core:
+        c4core_amalgamated = "src/c4/c4core_all.hpp"
+        am_c4core.amalgamate_c4core(f"{projdir}/{c4core_amalgamated}",
+                                    with_fastfloat=with_fastfloat,
+                                    with_stl=with_stl)
+    repo = "https://github.com/biojppm/rapidyaml"
+    ryml_preamble = f"""
 Rapid YAML - a library to parse and emit YAML, and do it fast.
 
 {repo}
@@ -56,19 +68,6 @@
     preprocessor symbol RYML_SHARED . This will take
     care of symbol export/import.
 """
-
-
-def amalgamate_ryml(filename: str,
-                    with_c4core: bool,
-                    with_fastfloat: bool,
-                    with_stl: bool):
-    c4core_amalgamated = ""
-    if with_c4core:
-        c4core_amalgamated = "src/c4/c4core_all.hpp"
-        am_c4core.amalgamate_c4core(f"{projdir}/{c4core_amalgamated}",
-                                    with_fastfloat=with_fastfloat,
-                                    with_stl=with_stl)
-    repo = "https://github.com/biojppm/rapidyaml"
     srcfiles = [
         am.cmttext(ryml_preamble),
         am.cmtfile("LICENSE.txt"),
@@ -94,7 +93,6 @@ def amalgamate_ryml(filename: str,
         am.onlyif(with_stl, "src/c4/yml/std/std.hpp"),
         "src/c4/yml/common.cpp",
         "src/c4/yml/tree.cpp",
-        "src/c4/yml/filter.def.hpp",
         "src/c4/yml/parse.cpp",
         "src/c4/yml/node.cpp",
         "src/c4/yml/preprocess.hpp",