diff --git a/cache.h b/cache.h
index 0f1f9dde56b..daf6150bb3c 100644
--- a/cache.h
+++ b/cache.h
@@ -1363,40 +1363,6 @@ struct object_context {
 	char *path;
 };
 
-#define GET_OID_QUIETLY           01
-#define GET_OID_COMMIT            02
-#define GET_OID_COMMITTISH        04
-#define GET_OID_TREE             010
-#define GET_OID_TREEISH          020
-#define GET_OID_BLOB             040
-#define GET_OID_FOLLOW_SYMLINKS 0100
-#define GET_OID_RECORD_PATH     0200
-#define GET_OID_ONLY_TO_DIE    04000
-#define GET_OID_REQUIRE_PATH  010000
-
-#define GET_OID_DISAMBIGUATORS \
-	(GET_OID_COMMIT | GET_OID_COMMITTISH | \
-	GET_OID_TREE | GET_OID_TREEISH | \
-	GET_OID_BLOB)
-
-enum get_oid_result {
-	FOUND = 0,
-	MISSING_OBJECT = -1, /* The requested object is missing */
-	SHORT_NAME_AMBIGUOUS = -2,
-	/* The following only apply when symlinks are followed */
-	DANGLING_SYMLINK = -4, /*
-				* The initial symlink is there, but
-				* (transitively) points to a missing
-				* in-tree file
-				*/
-	SYMLINK_LOOP = -5,
-	NOT_DIR = -6, /*
-		       * Somewhere along the symlink chain, a path is
-		       * requested which contains a file as a
-		       * non-final element.
-		       */
-};
-
 int repo_get_oid(struct repository *r, const char *str, struct object_id *oid);
 __attribute__((format (printf, 2, 3)))
 int get_oidf(struct object_id *oid, const char *fmt, ...);
diff --git a/diffcore.h b/diffcore.h
index 9b588a1ee15..1701ed50b9c 100644
--- a/diffcore.h
+++ b/diffcore.h
@@ -4,9 +4,11 @@
 #ifndef DIFFCORE_H
 #define DIFFCORE_H
 
-#include "cache.h"
+#include "hash.h"
 
 struct diff_options;
+struct mem_pool;
+struct oid_array;
 struct repository;
 struct strintmap;
 struct strmap;
diff --git a/hash.h b/hash.h
index 351afc2ce3b..d39f73618cb 100644
--- a/hash.h
+++ b/hash.h
@@ -123,6 +123,40 @@ struct object_id {
 	int algo;	/* XXX requires 4-byte alignment */
 };
 
+#define GET_OID_QUIETLY           01
+#define GET_OID_COMMIT            02
+#define GET_OID_COMMITTISH        04
+#define GET_OID_TREE             010
+#define GET_OID_TREEISH          020
+#define GET_OID_BLOB             040
+#define GET_OID_FOLLOW_SYMLINKS 0100
+#define GET_OID_RECORD_PATH     0200
+#define GET_OID_ONLY_TO_DIE    04000
+#define GET_OID_REQUIRE_PATH  010000
+
+#define GET_OID_DISAMBIGUATORS \
+	(GET_OID_COMMIT | GET_OID_COMMITTISH | \
+	GET_OID_TREE | GET_OID_TREEISH | \
+	GET_OID_BLOB)
+
+enum get_oid_result {
+	FOUND = 0,
+	MISSING_OBJECT = -1, /* The requested object is missing */
+	SHORT_NAME_AMBIGUOUS = -2,
+	/* The following only apply when symlinks are followed */
+	DANGLING_SYMLINK = -4, /*
+				* The initial symlink is there, but
+				* (transitively) points to a missing
+				* in-tree file
+				*/
+	SYMLINK_LOOP = -5,
+	NOT_DIR = -6, /*
+		       * Somewhere along the symlink chain, a path is
+		       * requested which contains a file as a
+		       * non-final element.
+		       */
+};
+
 /* A suitably aligned type for stack allocations of hash contexts. */
 union git_hash_ctx {
 	git_SHA_CTX sha1;
diff --git a/line-log.h b/line-log.h
index 82ae8d98a40..adff361b1bc 100644
--- a/line-log.h
+++ b/line-log.h
@@ -5,6 +5,7 @@
 
 struct rev_info;
 struct commit;
+struct string_list;
 
 /* A range [start,end].  Lines are numbered starting at 0, and the
  * ranges include start but exclude end. */
diff --git a/submodule-config.h b/submodule-config.h
index 28a8ca6bf46..c2045875bbb 100644
--- a/submodule-config.h
+++ b/submodule-config.h
@@ -1,7 +1,6 @@
 #ifndef SUBMODULE_CONFIG_CACHE_H
 #define SUBMODULE_CONFIG_CACHE_H
 
-#include "cache.h"
 #include "config.h"
 #include "hashmap.h"
 #include "submodule.h"
diff --git a/t/helper/test-submodule-nested-repo-config.c b/t/helper/test-submodule-nested-repo-config.c
index dc1c14bde37..a3848a8b668 100644
--- a/t/helper/test-submodule-nested-repo-config.c
+++ b/t/helper/test-submodule-nested-repo-config.c
@@ -1,4 +1,5 @@
 #include "test-tool.h"
+#include "cache.h"
 #include "submodule-config.h"
 
 static void die_usage(const char **argv, const char *msg)
diff --git a/tree-walk.h b/tree-walk.h
index 6305d531503..25fe27e3529 100644
--- a/tree-walk.h
+++ b/tree-walk.h
@@ -1,7 +1,9 @@
 #ifndef TREE_WALK_H
 #define TREE_WALK_H
 
-#include "cache.h"
+#include "hash.h"
+
+struct index_state;
 
 #define MAX_TRAVERSE_TREES 8