diff --git a/fitz/helper-devices.i b/fitz/helper-devices.i
index 949a70dac..7d9e92396 100644
--- a/fitz/helper-devices.i
+++ b/fitz/helper-devices.i
@@ -610,9 +610,9 @@ jm_trace_text_span(fz_context *ctx, PyObject *out, fz_text_span *span, int type,
 	PyObject *chars = PyTuple_New(span->len);
 	fz_matrix mat = fz_concat(span->trm, ctm); // text transformation matrix
 	fz_point dir = fz_transform_vector(fz_make_point(1, 0), mat); // writing direction
-	dir = fz_normalize_vector(dir);
+	double fsize = sqrt(dir.x * dir.x + dir.y * dir.y);
 
-	double fsize = sqrt(fabs((double) span->trm.a * (double) span->trm.d)); // font size
+	dir = fz_normalize_vector(dir);
 	double linewidth, adv, asc, dsc;
 	double space_adv = 0;
 	float x0, y0, x1, y1;
diff --git a/src/__init__.py b/src/__init__.py
index fcda0fbb1..970239096 100644
--- a/src/__init__.py
+++ b/src/__init__.py
@@ -17895,9 +17895,9 @@ def jm_trace_text_span(dev, span, type_, ctm, colorspace, color, alpha, seqno):
     
     mat = mupdf.fz_concat(span.trm(), ctm)  # text transformation matrix
     dir = mupdf.fz_transform_vector(mupdf.fz_make_point(1, 0), mat) # writing direction
-    dir = mupdf.fz_normalize_vector(dir)
+    fsize = math.sqrt(dir.x * dir.x + dir.y * dir.y) # font size
 
-    fsize = math.sqrt(abs(span.trm().a * span.trm().d)) # font size
+    dir = mupdf.fz_normalize_vector(dir)
 
     space_adv = 0;
     asc = JM_font_ascender( span.font())
diff --git a/src/extra.i b/src/extra.i
index 13a756530..f9ce90328 100644
--- a/src/extra.i
+++ b/src/extra.i
@@ -1997,9 +1997,9 @@ static void jm_trace_text_span(
     //double fsize = sqrt(fabs((double) span->trm.a * (double) span->trm.d));
     fz_matrix mat = mupdf::ll_fz_concat(span->trm, ctm); // text transformation matrix
     fz_point dir = mupdf::ll_fz_transform_vector(mupdf::ll_fz_make_point(1, 0), mat); // writing direction
-    dir = mupdf::ll_fz_normalize_vector(dir);
+    double fsize = sqrt(dir.x * dir.x + dir.y * dir.y); // font size
 
-    double fsize = sqrt(fabs((double) span->trm.a * (double) span->trm.d)); // font size
+    dir = mupdf::ll_fz_normalize_vector(dir);
 
     // compute effective ascender / descender
     double asc = (double) JM_font_ascender(span->font);
diff --git a/tests/resources/test_2645_1.pdf b/tests/resources/test_2645_1.pdf
new file mode 100644
index 000000000..5c177a094
Binary files /dev/null and b/tests/resources/test_2645_1.pdf differ
diff --git a/tests/resources/test_2645_2.pdf b/tests/resources/test_2645_2.pdf
new file mode 100644
index 000000000..0a9317a52
Binary files /dev/null and b/tests/resources/test_2645_2.pdf differ
diff --git a/tests/resources/test_2645_3.pdf b/tests/resources/test_2645_3.pdf
new file mode 100644
index 000000000..199089988
Binary files /dev/null and b/tests/resources/test_2645_3.pdf differ
diff --git a/tests/test_general.py b/tests/test_general.py
index 76e62241d..e7dcdb517 100644
--- a/tests/test_general.py
+++ b/tests/test_general.py
@@ -277,6 +277,21 @@ def test_2533():
     assert page.search_for(NEEDLE)[0] == bbox
 
 
+def test_2645():
+    """Assert same font size calculation in corner cases.
+    """
+    folder = os.path.join(scriptdir, "resources")
+    files = ("test_2645_1.pdf", "test_2645_2.pdf", "test_2645_3.pdf")
+    for f in files:
+        doc = fitz.open(os.path.join(folder, f))
+        page = doc[0]
+        fontsize0 = page.get_texttrace()[0]["size"]
+        fontsize1 = page.get_text("dict", flags=fitz.TEXTFLAGS_TEXT)["blocks"][0]["lines"][
+            0
+        ]["spans"][0]["size"]
+        assert abs(fontsize0 - fontsize1) < 1e-5
+
+
 def test_2506():
     """Ensure expected font size across text writing angles."""
     doc = fitz.open()