diff --git a/src/libfetchers/fs-input-accessor.cc b/src/libfetchers/fs-input-accessor.cc
index 3444c4643..7638d2d82 100644
--- a/src/libfetchers/fs-input-accessor.cc
+++ b/src/libfetchers/fs-input-accessor.cc
@@ -1,4 +1,5 @@
 #include "fs-input-accessor.hh"
+#include "posix-source-accessor.hh"
 #include "store-api.hh"
 
 namespace nix {
diff --git a/src/libutil/archive.cc b/src/libutil/archive.cc
index 0cd54e5db..3b1a1e0ef 100644
--- a/src/libutil/archive.cc
+++ b/src/libutil/archive.cc
@@ -14,7 +14,7 @@
 #include "archive.hh"
 #include "util.hh"
 #include "config.hh"
-#include "source-accessor.hh"
+#include "posix-source-accessor.hh"
 
 namespace nix {
 
diff --git a/src/libutil/posix-source-accessor.cc b/src/libutil/posix-source-accessor.cc
new file mode 100644
index 000000000..48b4fe626
--- /dev/null
+++ b/src/libutil/posix-source-accessor.cc
@@ -0,0 +1,86 @@
+#include "posix-source-accessor.hh"
+
+namespace nix {
+
+void PosixSourceAccessor::readFile(
+    const CanonPath & path,
+    Sink & sink,
+    std::function<void(uint64_t)> sizeCallback)
+{
+    // FIXME: add O_NOFOLLOW since symlinks should be resolved by the
+    // caller?
+    AutoCloseFD fd = open(path.c_str(), O_RDONLY | O_CLOEXEC);
+    if (!fd)
+        throw SysError("opening file '%1%'", path);
+
+    struct stat st;
+    if (fstat(fd.get(), &st) == -1)
+        throw SysError("statting file");
+
+    sizeCallback(st.st_size);
+
+    off_t left = st.st_size;
+
+    std::vector<unsigned char> buf(64 * 1024);
+    while (left) {
+        checkInterrupt();
+        ssize_t rd = read(fd.get(), buf.data(), (size_t) std::min(left, (off_t) buf.size()));
+        if (rd == -1) {
+            if (errno != EINTR)
+                throw SysError("reading from file '%s'", showPath(path));
+        }
+        else if (rd == 0)
+            throw SysError("unexpected end-of-file reading '%s'", showPath(path));
+        else {
+            assert(rd <= left);
+            sink({(char *) buf.data(), (size_t) rd});
+            left -= rd;
+        }
+    }
+}
+
+bool PosixSourceAccessor::pathExists(const CanonPath & path)
+{
+    return nix::pathExists(path.abs());
+}
+
+SourceAccessor::Stat PosixSourceAccessor::lstat(const CanonPath & path)
+{
+    auto st = nix::lstat(path.abs());
+    mtime = std::max(mtime, st.st_mtime);
+    return Stat {
+        .type =
+            S_ISREG(st.st_mode) ? tRegular :
+            S_ISDIR(st.st_mode) ? tDirectory :
+            S_ISLNK(st.st_mode) ? tSymlink :
+            tMisc,
+        .isExecutable = S_ISREG(st.st_mode) && st.st_mode & S_IXUSR
+    };
+}
+
+SourceAccessor::DirEntries PosixSourceAccessor::readDirectory(const CanonPath & path)
+{
+    DirEntries res;
+    for (auto & entry : nix::readDirectory(path.abs())) {
+        std::optional<Type> type;
+        switch (entry.type) {
+        case DT_REG: type = Type::tRegular; break;
+        case DT_LNK: type = Type::tSymlink; break;
+        case DT_DIR: type = Type::tDirectory; break;
+        }
+        res.emplace(entry.name, type);
+    }
+    return res;
+}
+
+std::string PosixSourceAccessor::readLink(const CanonPath & path)
+{
+    return nix::readLink(path.abs());
+}
+
+std::optional<CanonPath> PosixSourceAccessor::getPhysicalPath(const CanonPath & path)
+{
+    return path;
+}
+
+}
diff --git a/src/libutil/posix-source-accessor.hh b/src/libutil/posix-source-accessor.hh
new file mode 100644
index 000000000..608f96ee2
--- /dev/null
+++ b/src/libutil/posix-source-accessor.hh
@@ -0,0 +1,34 @@
+#pragma once
+
+#include "source-accessor.hh"
+
+namespace nix {
+
+/**
+ * A source accessor that uses the Unix filesystem.
+ */
+struct PosixSourceAccessor : SourceAccessor
+{
+    /**
+     * The most recent mtime seen by lstat(). This is a hack to
+     * support dumpPathAndGetMtime(). Should remove this eventually.
+     */
+    time_t mtime = 0;
+
+    void readFile(
+        const CanonPath & path,
+        Sink & sink,
+        std::function<void(uint64_t)> sizeCallback) override;
+
+    bool pathExists(const CanonPath & path) override;
+
+    Stat lstat(const CanonPath & path) override;
+
+    DirEntries readDirectory(const CanonPath & path) override;
+
+    std::string readLink(const CanonPath & path) override;
+
+    std::optional<CanonPath> getPhysicalPath(const CanonPath & path) override;
+};
+
+}
diff --git a/src/libutil/source-accessor.cc b/src/libutil/source-accessor.cc
index 2d03d3d7a..d168a9667 100644
--- a/src/libutil/source-accessor.cc
+++ b/src/libutil/source-accessor.cc
@@ -55,85 +55,4 @@ std::string SourceAccessor::showPath(const CanonPath & path)
     return path.abs();
 }
 
-void PosixSourceAccessor::readFile(
-    const CanonPath & path,
-    Sink & sink,
-    std::function<void(uint64_t)> sizeCallback)
-{
-    // FIXME: add O_NOFOLLOW since symlinks should be resolved by the
-    // caller?
-    AutoCloseFD fd = open(path.c_str(), O_RDONLY | O_CLOEXEC);
-    if (!fd)
-        throw SysError("opening file '%1%'", path);
-
-    struct stat st;
-    if (fstat(fd.get(), &st) == -1)
-        throw SysError("statting file");
-
-    sizeCallback(st.st_size);
-
-    off_t left = st.st_size;
-
-    std::vector<unsigned char> buf(64 * 1024);
-    while (left) {
-        checkInterrupt();
-        ssize_t rd = read(fd.get(), buf.data(), (size_t) std::min(left, (off_t) buf.size()));
-        if (rd == -1) {
-            if (errno != EINTR)
-                throw SysError("reading from file '%s'", showPath(path));
-        }
-        else if (rd == 0)
-            throw SysError("unexpected end-of-file reading '%s'", showPath(path));
-        else {
-            assert(rd <= left);
-            sink({(char *) buf.data(), (size_t) rd});
-            left -= rd;
-        }
-    }
-}
-
-bool PosixSourceAccessor::pathExists(const CanonPath & path)
-{
-    return nix::pathExists(path.abs());
-}
-
-SourceAccessor::Stat PosixSourceAccessor::lstat(const CanonPath & path)
-{
-    auto st = nix::lstat(path.abs());
-    mtime = std::max(mtime, st.st_mtime);
-    return Stat {
-        .type =
-            S_ISREG(st.st_mode) ? tRegular :
-            S_ISDIR(st.st_mode) ? tDirectory :
-            S_ISLNK(st.st_mode) ? tSymlink :
-            tMisc,
-        .isExecutable = S_ISREG(st.st_mode) && st.st_mode & S_IXUSR
-    };
-}
-
-SourceAccessor::DirEntries PosixSourceAccessor::readDirectory(const CanonPath & path)
-{
-    DirEntries res;
-    for (auto & entry : nix::readDirectory(path.abs())) {
-        std::optional<Type> type;
-        switch (entry.type) {
-        case DT_REG: type = Type::tRegular; break;
-        case DT_LNK: type = Type::tSymlink; break;
-        case DT_DIR: type = Type::tDirectory; break;
-        }
-        res.emplace(entry.name, type);
-    }
-    return res;
-}
-
-std::string PosixSourceAccessor::readLink(const CanonPath & path)
-{
-    return nix::readLink(path.abs());
-}
-
-std::optional<CanonPath> PosixSourceAccessor::getPhysicalPath(const CanonPath & path)
-{
-    return path;
-}
-
 }
diff --git a/src/libutil/source-accessor.hh b/src/libutil/source-accessor.hh
index f3504c9bb..fd823aa39 100644
--- a/src/libutil/source-accessor.hh
+++ b/src/libutil/source-accessor.hh
@@ -104,31 +104,4 @@ struct SourceAccessor
     virtual std::string showPath(const CanonPath & path);
 };
 
-/**
- * A source accessor that uses the Unix filesystem.
- */
-struct PosixSourceAccessor : SourceAccessor
-{
-    /**
-     * The most recent mtime seen by lstat(). This is a hack to
-     * support dumpPathAndGetMtime(). Should remove this eventually.
-     */
-    time_t mtime = 0;
-
-    void readFile(
-        const CanonPath & path,
-        Sink & sink,
-        std::function<void(uint64_t)> sizeCallback) override;
-
-    bool pathExists(const CanonPath & path) override;
-
-    Stat lstat(const CanonPath & path) override;
-
-    DirEntries readDirectory(const CanonPath & path) override;
-
-    std::string readLink(const CanonPath & path) override;
-
-    std::optional<CanonPath> getPhysicalPath(const CanonPath & path) override;
-};
-
 }