diff --git a/sw/qa/core/layout/data/fly-rel-width-rounding.odt b/sw/qa/core/layout/data/fly-rel-width-rounding.odt
new file mode 100644
index 000000000000..b70b9e51a917
Binary files /dev/null and b/sw/qa/core/layout/data/fly-rel-width-rounding.odt differ
diff --git a/sw/qa/core/layout/fly.cxx b/sw/qa/core/layout/fly.cxx
index 47cfb40fa6e7..81df20af3b35 100644
--- a/sw/qa/core/layout/fly.cxx
+++ b/sw/qa/core/layout/fly.cxx
@@ -86,6 +86,31 @@ CPPUNIT_TEST_FIXTURE(Test, testSplitFlyNegativeHeight)
         }
     }
 }
+
+CPPUNIT_TEST_FIXTURE(Test, testFlyRelWithRounding)
+{
+    // Given a document where page width is 21.001cm (11906 twips), and the image width is 48% of
+    // the page width:
+    createSwDoc("fly-rel-width-rounding.odt");
+
+    // When laying out that document:
+    SwDoc* pDoc = getSwDoc();
+    SwRootFrame* pLayout = pDoc->getIDocumentLayoutAccess().GetCurrentLayout();
+
+    // Then make sure that we calculate the width of the fly correctly:
+    auto pPage = pLayout->GetLower()->DynCastPageFrame();
+    CPPUNIT_ASSERT(pPage->GetSortedObjs());
+    SwSortedObjs& rPageObjs = *pPage->GetSortedObjs();
+    CPPUNIT_ASSERT_EQUAL(static_cast<size_t>(1), rPageObjs.size());
+    auto pFly = rPageObjs[0]->DynCastFlyFrame()->DynCastFlyAtContentFrame();
+    CPPUNIT_ASSERT(pFly);
+    tools::Long nFlyWidth = pFly->getFrameArea().Width();
+    // Without the accompanying fix in place, this test would have failed with:
+    // - Expected: 5715
+    // - Actual  : 5714
+    // i.e. 5714.88 was truncated, not rounded.
+    CPPUNIT_ASSERT_EQUAL(static_cast<tools::Long>(5715), nFlyWidth);
+}
 }
 
 /* vim:set shiftwidth=4 softtabstop=4 expandtab: */
diff --git a/sw/source/core/layout/fly.cxx b/sw/source/core/layout/fly.cxx
index 549681ca7227..a3c9ac84e7c2 100644
--- a/sw/source/core/layout/fly.cxx
+++ b/sw/source/core/layout/fly.cxx
@@ -70,6 +70,7 @@
 #include <basegfx/matrix/b2dhommatrixtools.hxx>
 #include <osl/diagnose.h>
 #include <o3tl/string_view.hxx>
+#include <rtl/math.hxx>
 
 #include <wrtsh.hxx>
 #include <view.hxx>
@@ -2845,9 +2846,9 @@ Size SwFlyFrame::CalcRel( const SwFormatFrameSize &rSz ) const
         }
 
         if ( rSz.GetWidthPercent() && rSz.GetWidthPercent() != SwFormatFrameSize::SYNCED )
-            aRet.setWidth( nRelWidth * rSz.GetWidthPercent() / 100 );
+            aRet.setWidth(rtl::math::round(double(nRelWidth) * rSz.GetWidthPercent() / 100));
         if ( rSz.GetHeightPercent() && rSz.GetHeightPercent() != SwFormatFrameSize::SYNCED )
-            aRet.setHeight( nRelHeight * rSz.GetHeightPercent() / 100 );
+            aRet.setHeight(rtl::math::round(double(nRelHeight) * rSz.GetHeightPercent() / 100));
 
         if ( rSz.GetHeight() && rSz.GetWidthPercent() == SwFormatFrameSize::SYNCED )
         {
diff --git a/xmloff/qa/unit/text.cxx b/xmloff/qa/unit/text.cxx
index 1679af04bc1f..f95e07e42578 100644
--- a/xmloff/qa/unit/text.cxx
+++ b/xmloff/qa/unit/text.cxx
@@ -508,11 +508,11 @@ CPPUNIT_TEST_FIXTURE(XmloffStyleTest, testRelativeWidth)
 
     xmlDocUniquePtr pXmlDoc = parseExport(u"content.xml"_ustr);
     // Without the accompanying fix in place, this failed with:
-    // - Expected: 3.1492in (8cm)
+    // - Expected: 3.15in (8cm)
     // - Actual  : 0.0161in (0.04 cm)
     // i.e. the fallback width value wasn't the expected half of the body frame width, but a smaller
     // value.
-    assertXPath(pXmlDoc, "//draw:frame"_ostr, "width"_ostr, u"3.1492in"_ustr);
+    assertXPath(pXmlDoc, "//draw:frame"_ostr, "width"_ostr, u"3.15in"_ustr);
 }
 
 CPPUNIT_TEST_FIXTURE(XmloffStyleTest, testScaleWidthAndHeight)