diff --git a/slither/core/declarations/contract.py b/slither/core/declarations/contract.py
index 2db1cd964..c70711502 100644
--- a/slither/core/declarations/contract.py
+++ b/slither/core/declarations/contract.py
@@ -78,6 +78,7 @@ class Contract(SourceMapping):  # pylint: disable=too-many-public-methods
         self._using_for: Dict[Union[str, Type], List[Type]] = {}
         self._kind: Optional[str] = None
         self._is_interface: bool = False
+        self._is_library: bool = False
 
         self._signatures: Optional[List[str]] = None
         self._signatures_declared: Optional[List[str]] = None
@@ -144,6 +145,14 @@ class Contract(SourceMapping):  # pylint: disable=too-many-public-methods
     def is_interface(self, is_interface: bool):
         self._is_interface = is_interface
 
+    @property
+    def is_library(self) -> bool:
+        return self._is_library
+
+    @is_library.setter
+    def is_library(self, is_library: bool):
+        self._is_library = is_library
+
     # endregion
     ###################################################################################
     ###################################################################################
diff --git a/slither/solc_parsing/declarations/contract.py b/slither/solc_parsing/declarations/contract.py
index efc53f2aa..8823112fb 100644
--- a/slither/solc_parsing/declarations/contract.py
+++ b/slither/solc_parsing/declarations/contract.py
@@ -157,6 +157,8 @@ class ContractSolc(CallerContextExpression):
         if "contractKind" in attributes:
             if attributes["contractKind"] == "interface":
                 self._contract.is_interface = True
+            elif attributes["contractKind"] == "library":
+                self._contract.is_library = True
             self._contract.kind = attributes["contractKind"]
         self._linearized_base_contracts = attributes["linearizedBaseContracts"]
         # self._contract.fullyImplemented = attributes["fullyImplemented"]
diff --git a/slither/tools/flattening/__main__.py b/slither/tools/flattening/__main__.py
index e0888f222..977b84896 100644
--- a/slither/tools/flattening/__main__.py
+++ b/slither/tools/flattening/__main__.py
@@ -79,6 +79,12 @@ def parse_args():
         action="store_true",
     )
 
+    group_patching.add_argument(
+        "--convert-library-to-internal",
+        help="Convert external or public functions to internal in library.",
+        action="store_true",
+    )
+
     group_patching.add_argument(
         "--remove-assert", help="Remove call to assert().", action="store_true"
     )
@@ -111,6 +117,7 @@ def main():
             compilation_unit,
             external_to_public=args.convert_external,
             remove_assert=args.remove_assert,
+            convert_library_to_internal=args.convert_library_to_internal,
             private_to_internal=args.convert_private,
             export_path=args.dir,
             pragma_solidity=args.pragma_solidity,
diff --git a/slither/tools/flattening/flattening.py b/slither/tools/flattening/flattening.py
index f067bde6d..90b751afb 100644
--- a/slither/tools/flattening/flattening.py
+++ b/slither/tools/flattening/flattening.py
@@ -51,6 +51,7 @@ class Flattening:
         compilation_unit: SlitherCompilationUnit,
         external_to_public=False,
         remove_assert=False,
+        convert_library_to_internal=False,
         private_to_internal=False,
         export_path: Optional[str] = None,
         pragma_solidity: Optional[str] = None,
@@ -61,6 +62,7 @@ class Flattening:
         self._external_to_public = external_to_public
         self._remove_assert = remove_assert
         self._use_abi_encoder_v2 = False
+        self._convert_library_to_internal = convert_library_to_internal
         self._private_to_internal = private_to_internal
         self._pragma_solidity = pragma_solidity
 
@@ -146,6 +148,40 @@ class Flattening:
                                 )
                             )
 
+        if self._convert_library_to_internal and contract.is_library:
+            for f in contract.functions_declared:
+                visibility = ""
+                if f.visibility == "external":
+                    visibility = f.visibility
+                elif f.visibility == "public":
+                    visibility = f.visibility
+
+                if visibility != "":
+                    attributes_start = (
+                        f.parameters_src().source_mapping["start"]
+                        + f.parameters_src().source_mapping["length"]
+                    )
+                    attributes_end = f.returns_src().source_mapping["start"]
+                    attributes = content[attributes_start:attributes_end]
+                    regex = (
+                        re.search(r"((\sexternal)\s+)|(\sexternal)$|(\)external)$", attributes)
+                        if visibility == "external"
+                        else re.search(r"((\spublic)\s+)|(\spublic)$|(\)public)$", attributes)
+                    )
+                    if regex:
+                        to_patch.append(
+                            Patch(
+                                attributes_start + regex.span()[0] + 1,
+                                "external_to_internal"
+                                if visibility == "external"
+                                else "public_to_internal",
+                            )
+                        )
+                    else:
+                        raise SlitherException(
+                            f"{visibility} keyword not found {f.name} {attributes}"
+                        )
+
         if self._private_to_internal:
             for variable in contract.state_variables_declared:
                 if variable.visibility == "private":
@@ -186,6 +222,10 @@ class Flattening:
             index = index - start
             if patch_type == "public_to_external":
                 content = content[:index] + "public" + content[index + len("external") :]
+            elif patch_type == "external_to_internal":
+                content = content[:index] + "internal" + content[index + len("external") :]
+            elif patch_type == "public_to_internal":
+                content = content[:index] + "internal" + content[index + len("public") :]
             elif patch_type == "private_to_internal":
                 content = content[:index] + "internal" + content[index + len("private") :]
             elif patch_type == "calldata_to_memory":