diff --git a/CMakeLists.txt b/CMakeLists.txt
index 2f34406..0c69498 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -4,7 +4,7 @@ project(ke C)  # Specify C language explicitly
 set(CMAKE_C_STANDARD 99)
 set(KE_VERSION "2.1.1")
 
-set(CMAKE_C_FLAGS "-Wall -Wextra -pedantic -Wshadow -Werror -std=c99 -g -Werror=stringop-truncation")
+set(CMAKE_C_FLAGS "-Wall -Wextra -pedantic -Wshadow -Werror -std=c99 -g")
 set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -D_DEFAULT_SOURCE -D_XOPEN_SOURCE")
 
 # Optionally enable AddressSanitizer (ASan)
@@ -19,16 +19,28 @@ endif()
 
 include(GNUInstallDirs)
 
-# Add executable
-add_executable(ke
+set(SOURCES
+        core.c
         abuf.c
         term.c
         buffer.c
         editor.c
-        core.c
-        core.h
+        undo.c
         main.c
 )
+
+set(HEADERS
+        core.h
+        abuf.h
+        term.h
+        buffer.h
+        editor.h
+        undo.h
+)
+
+
+# Add executable
+add_executable(ke ${SOURCES} ${HEADERS})
 target_compile_definitions(ke PRIVATE KE_VERSION="ke version ${KE_VERSION}")
 install(TARGETS ke RUNTIME DESTINATION bin)
 install(FILES ke.1 TYPE MAN)
diff --git a/Makefile b/Makefile
index 92f718a..4c8771b 100644
--- a/Makefile
+++ b/Makefile
@@ -11,8 +11,8 @@ LDFLAGS :=	-fsanitize=address
 
 all: $(TARGET) test.txt
 
-SRCS := main.c abuf.c term.c buffer.c editor.c core.c
-HDRS :=        abuf.h term.h buffer.h editor.h core.h
+SRCS := main.c abuf.c core.c term.c buffer.c editor.c undo.c
+HDRS :=        abuf.h core.h term.h buffer.h editor.h undo.h
 
 $(TARGET): $(SRCS)
 	$(CC) $(CFLAGS) -o $(TARGET) $(SRCS) $(LDFLAGS)
diff --git a/abuf.c b/abuf.c
index a1f0dd5..c302cb0 100644
--- a/abuf.c
+++ b/abuf.c
@@ -71,6 +71,13 @@ ab_append(abuf *buf, const char *s, size_t len)
 }
 
 
+void
+ab_append_ab(abuf *buf, const abuf *other)
+{
+	ab_append(buf, other->b, other->size);
+}
+
+
 void
 ab_prependch(abuf *buf, const char c)
 {
diff --git a/abuf.h b/abuf.h
index 90d87f3..96fcec6 100644
--- a/abuf.h
+++ b/abuf.h
@@ -22,8 +22,10 @@ void		 ab_init_cap(abuf *buf, size_t cap);
 void		 ab_resize(abuf *buf, size_t cap);
 void		 ab_appendch(abuf *buf, char c);
 void		 ab_append(abuf *buf, const char *s, size_t len);
+void		 ab_append_ab(abuf *buf, const abuf *other);
 void		 ab_prependch(abuf *buf, const char c);
 void		 ab_prepend(abuf *buf, const char *s, const size_t len);
+void		 ab_prepend_ab(abuf *buf, const abuf *other);
 void		 ab_free(abuf *buf);
 
 
diff --git a/buffer.h b/buffer.h
index 1289801..0d6ea6c 100644
--- a/buffer.h
+++ b/buffer.h
@@ -2,20 +2,23 @@
 #define KE_BUFFER_H
 
 #include "abuf.h"
+#include "undo.h"
 
 
 typedef struct buffer {
-	size_t	 curx, cury;
-	size_t	 rx;
-	size_t	 nrows;
-	size_t	 rowoffs, coloffs;
-	abuf	*row;
-	char	*filename;
-	int	 dirty;
-	int	 mark_set;
-	size_t	 mark_curx, mark_cury;
+	size_t		 curx, cury;
+	size_t		 rx;
+	size_t		 nrows;
+	size_t		 rowoffs, coloffs;
+	abuf		*row;
+	char		*filename;
+	int		 dirty;
+	int		 mark_set;
+	size_t		 mark_curx, mark_cury;
+	undo_tree	 tree;
 } buffer;
 
+
 /* Access current buffer and convenient aliases for file-specific fields */
 buffer		*buffer_current(void);
 
diff --git a/core.h b/core.h
index f2d0c3b..0e400ca 100644
--- a/core.h
+++ b/core.h
@@ -36,4 +36,4 @@ void		 kwrite(int fd, const char *buf, int len);
 void		 die(const char *s);
 
 
-#endif
\ No newline at end of file
+#endif
diff --git a/undo.c b/undo.c
index 50551c8..fa07057 100644
--- a/undo.c
+++ b/undo.c
@@ -27,8 +27,6 @@ undo_node_new(undo_kind kind)
 void
 undo_node_free(undo_node *node)
 {
-	undo_node	*next = NULL;
-
 	if (node == NULL) {
 		return;
 	}
@@ -100,15 +98,56 @@ undo_begin(undo_tree *tree, undo_kind kind)
 void
 undo_prepend(undo_tree *tree, abuf *buf)
 {
+	assert(tree != NULL);
+	assert(tree->pending != NULL);
+
+	ab_prepend_ab(tree->pending->text, buf);
+}
+
+
+void
+undo_append(undo_tree *tree, abuf *buf)
+{
+	assert(tree != NULL);
+	assert(tree->pending != NULL);
+
+	ab_append_ab(tree->pending->text, buf);
+}
+
+
+void
+undo_prependch(undo_tree *tree, char c)
+{
+	assert(tree != NULL);
+	assert(tree->pending != NULL);
+
+	ab_prependch(tree->pending->text, c);
+}
+
+
+void
+undo_appendch(undo_tree *tree, char c)
+{
+	assert(tree != NULL);
+	assert(tree->pending != NULL);
+
+	ab_appendch(tree->pending->text, c);
+}
+
+
+void
+undo_commit(undo_tree *tree)
+{
+	assert(tree != NULL);
+
+	if (tree->pending == NULL) {
+		return;
+	}
+
 
 }
 
 
-void		 undo_append(undo_tree *tree, abuf *buf);
-void		 undo_prependch(undo_tree *tree, char c);
-void		 undo_appendch(undo_tree *tree, char c);
-void		 undo_commit(undo_tree *tree);
-void		 undo_apply(struct editor *editor);
-void		 editor_undo(undo_tree *tree);
-void		 editor_redo(undo_tree *tree);
-
+void		 undo_apply(struct buffer *buf);
+void		 editor_undo(struct buffer *buf);
+void		 editor_redo(struct buffer *buf);
diff --git a/undo.h b/undo.h
index f33e5f5..198e47e 100644
--- a/undo.h
+++ b/undo.h
@@ -1,13 +1,15 @@
 #include <stddef.h>
 
 #include "abuf.h"
-#include "editor.h"
 
 
 #ifndef KE_UNDO_H
 #define KE_UNDO_H
 
 
+struct	 buffer;
+
+
 typedef enum undo_kind {
 	UNDO_INSERT  = 1 << 0,
 	UNDO_UNKNOWN = 1 << 1,
@@ -42,9 +44,9 @@ void		 undo_append(undo_tree *tree, abuf *buf);
 void		 undo_prependch(undo_tree *tree, char c);
 void		 undo_appendch(undo_tree *tree, char c);
 void		 undo_commit(undo_tree *tree);
-void		 undo_apply(struct editor *editor);
-void		 editor_undo(undo_tree *tree);
-void		 editor_redo(undo_tree *tree);
+void		 undo_apply(struct buffer *buf);
+void		 editor_undo(struct buffer *buf);
+void		 editor_redo(struct buffer *buf);
 
 
 #endif