diff --git a/src/libutil-tests/util.cc b/src/libutil-tests/util.cc
index c48b97e8e..32114d9da 100644
--- a/src/libutil-tests/util.cc
+++ b/src/libutil-tests/util.cc
@@ -158,6 +158,7 @@ TEST(renderSize, misc)
     ASSERT_EQ(renderSize(972, true), "   0.9 KiB");
     ASSERT_EQ(renderSize(973, true), "   1.0 KiB"); // FIXME: should round down
     ASSERT_EQ(renderSize(1024, true), "   1.0 KiB");
+    ASSERT_EQ(renderSize(-1024, true), "  -1.0 KiB");
     ASSERT_EQ(renderSize(1024 * 1024, true), "1024.0 KiB");
     ASSERT_EQ(renderSize(1100 * 1024, true), "   1.1 MiB");
     ASSERT_EQ(renderSize(2ULL * 1024 * 1024 * 1024, true), "   2.0 GiB");
diff --git a/src/libutil/include/nix/util/util.hh b/src/libutil/include/nix/util/util.hh
index 26f03938a..cb1c9694d 100644
--- a/src/libutil/include/nix/util/util.hh
+++ b/src/libutil/include/nix/util/util.hh
@@ -104,7 +104,7 @@ N string2IntWithUnitPrefix(std::string_view s)
  * GiB`. If `align` is set, the number will be right-justified by
  * padding with spaces on the left.
  */
-std::string renderSize(uint64_t value, bool align = false);
+std::string renderSize(int64_t value, bool align = false);
 
 /**
  * Parse a string into a float.
diff --git a/src/libutil/util.cc b/src/libutil/util.cc
index 383a904ad..69826070c 100644
--- a/src/libutil/util.cc
+++ b/src/libutil/util.cc
@@ -132,15 +132,16 @@ std::optional<N> string2Float(const std::string_view s)
 template std::optional<double> string2Float<double>(const std::string_view s);
 template std::optional<float> string2Float<float>(const std::string_view s);
 
-std::string renderSize(uint64_t value, bool align)
+std::string renderSize(int64_t value, bool align)
 {
     static const std::array<char, 9> prefixes{{'K', 'K', 'M', 'G', 'T', 'P', 'E', 'Z', 'Y'}};
     size_t power = 0;
-    double res = value;
-    while (res > 1024 && power < prefixes.size()) {
+    double abs_value = std::abs(value);
+    while (abs_value > 1024 && power < prefixes.size()) {
         ++power;
-        res /= 1024;
+        abs_value /= 1024;
     }
+    double res = (double) value / std::pow(1024.0, power);
     return fmt(align ? "%6.1f %ciB" : "%.1f %ciB", power == 0 ? res / 1024 : res, prefixes.at(power));
 }
 
diff --git a/src/nix/diff-closures.cc b/src/nix/diff-closures.cc
index cbf842e5c..d36a21d74 100644
--- a/src/nix/diff-closures.cc
+++ b/src/nix/diff-closures.cc
@@ -107,8 +107,7 @@ void printClosureDiff(
             if (!removed.empty() || !added.empty())
                 items.push_back(fmt("%s → %s", showVersions(removed), showVersions(added)));
             if (showDelta)
-                items.push_back(
-                    fmt("%s%+.1f KiB" ANSI_NORMAL, sizeDelta > 0 ? ANSI_RED : ANSI_GREEN, sizeDelta / 1024.0));
+                items.push_back(fmt("%s%s" ANSI_NORMAL, sizeDelta > 0 ? ANSI_RED : ANSI_GREEN, renderSize(sizeDelta)));
             logger->cout("%s%s: %s", indent, name, concatStringsSep(", ", items));
         }
     }
diff --git a/src/nix/path-info.cc b/src/nix/path-info.cc
index fef3ae120..146b775e5 100644
--- a/src/nix/path-info.cc
+++ b/src/nix/path-info.cc
@@ -141,7 +141,7 @@ struct CmdPathInfo : StorePathsCommand, MixJSON
     void printSize(std::ostream & str, uint64_t value)
     {
         if (humanReadable)
-            str << fmt("\t%s", renderSize(value, true));
+            str << fmt("\t%s", renderSize((int64_t) value, true));
         else
             str << fmt("\t%11d", value);
     }