diff --git a/read-cache.c b/read-cache.c
index f1f789b7b8..ac0fc80e77 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -608,6 +608,29 @@ int add_to_index(struct index_state *istate, const char *path, struct stat *st,
 		ce->ce_mode = ce_mode_from_stat(ent, st_mode);
 	}
 
+	/* When core.ignorecase=true, determine if a directory of the same name but differing
+	 * case already exists within the Git repository.  If it does, ensure the directory
+	 * case of the file being added to the repository matches (is folded into) the existing
+	 * entry's directory case.
+	 */
+	if (ignore_case) {
+		const char *startPtr = ce->name;
+		const char *ptr = startPtr;
+		while (*ptr) {
+			while (*ptr && *ptr != '/')
+				++ptr;
+			if (*ptr == '/') {
+				struct cache_entry *foundce;
+				++ptr;
+				foundce = index_name_exists(&the_index, ce->name, ptr - ce->name, ignore_case);
+				if (foundce) {
+					memcpy((void *)startPtr, foundce->name + (startPtr - ce->name), ptr - startPtr);
+					startPtr = ptr;
+				}
+			}
+		}
+	}
+
 	alias = index_name_exists(istate, ce->name, ce_namelen(ce), ignore_case);
 	if (alias && !ce_stage(alias) && !ie_match_stat(istate, alias, st, ce_option)) {
 		/* Nothing changed, really */