diff --git a/git-compat-util.h b/git-compat-util.h
index 58cdc087fa..51823ae7af 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -185,6 +185,12 @@ extern int git_munmap(void *start, size_t length);
 #define pread git_pread
 extern ssize_t git_pread(int fd, void *buf, size_t count, off_t offset);
 #endif
+/*
+ * Forward decl that will remind us if its twin in cache.h changes.
+ * This function is used in compat/pread.c.  But we can't include
+ * cache.h there.
+ */
+extern ssize_t read_in_full(int fd, void *buf, size_t count);
 
 #ifdef NO_SETENV
 #define setenv gitsetenv