diff --git a/dust_extinction/shapes.py b/dust_extinction/shapes.py
index 3ae5b8e..33f3cee 100644
--- a/dust_extinction/shapes.py
+++ b/dust_extinction/shapes.py
@@ -233,12 +233,13 @@ class FM90(Fittable1DModel):
     n_inputs = 1
     n_outputs = 1
 
-    C1 = Parameter(description="linear term: y-intercept", default=0.10)
-    C2 = Parameter(description="linear term: slope", default=0.70)
-    C3 = Parameter(description="bump: amplitude", default=3.23)
-    C4 = Parameter(description="FUV rise: amplitude", default=0.41)
-    xo = Parameter(description="bump: centroid", default=4.60, min=0.0)
-    gamma = Parameter(description="bump: width", default=0.99, min=0.0)
+    # bounds based on Gordon et al. (2024) results
+    C1 = Parameter(description="linear term: y-intercept", default=0.10, bounds=(-10.0, 5.0))
+    C2 = Parameter(description="linear term: slope", default=0.70, bounds=(-0.1, 5.0))
+    C3 = Parameter(description="bump: amplitude", default=3.23, bounds=(-1.0, 6.0))
+    C4 = Parameter(description="FUV rise: amplitude", default=0.41, bounds=(-0.5, 1.5))
+    xo = Parameter(description="bump: centroid", default=4.59, bounds=(4.5, 4.9))
+    gamma = Parameter(description="bump: width", default=0.95, bounds=(0.6, 1.7))
 
     x_range = x_range_FM90
 
@@ -400,12 +401,13 @@ class FM90_B3(Fittable1DModel):
     n_inputs = 1
     n_outputs = 1
 
-    C1 = Parameter(description="linear term: y-intercept", default=0.10)
-    C2 = Parameter(description="linear term: slope", default=0.70)
-    B3 = Parameter(description="bump: amplitude", default=3.23)
-    C4 = Parameter(description="FUV rise: amplitude", default=0.41)
-    xo = Parameter(description="bump: centroid", default=4.60, min=0.0)
-    gamma = Parameter(description="bump: width", default=0.99, min=0.0)
+    # bounds based on Gordon et al. (2024) results
+    C1 = Parameter(description="linear term: y-intercept", default=0.10, bounds=(-10.0, 5.0))
+    C2 = Parameter(description="linear term: slope", default=0.70, bounds=(-0.1, 5.0))
+    B3 = Parameter(description="bump: amplitude", default=3.23, bounds=(-1.0, 6.0))
+    C4 = Parameter(description="FUV rise: amplitude", default=0.41, bounds=(-0.5, 1.5))
+    xo = Parameter(description="bump: centroid", default=4.59, bounds=(4.5, 4.9))
+    gamma = Parameter(description="bump: width", default=0.95, bounds=(0.6, 1.7))
 
     x_range = x_range_FM90
 
diff --git a/dust_extinction/tests/test_fm90.py b/dust_extinction/tests/test_fm90.py
index a7c04b2..30dd842 100644
--- a/dust_extinction/tests/test_fm90.py
+++ b/dust_extinction/tests/test_fm90.py
@@ -16,18 +16,10 @@ def get_elvebv_cor_vals():
     x = x / u.micron
 
     # correct values
-    cor_vals = np.array(
-        [
-            2.9829317,
-            4.1215415,
-            6.4135842,
-            5.6574243,
-            4.7573250,
-            5.4905843,
-            9.2853567,
-            12.462238,
-        ]
-    )
+    # fmt: off
+    cor_vals = np.array([2.995507, 4.187955, 6.70251, 5.723752, 4.757428,
+                         5.490276, 9.285265, 12.462183])
+    # fmt: on
 
     return (x, cor_vals)
 
@@ -93,15 +85,9 @@ def test_FM90_fitting():
         g03_fit.gamma.value,
     ]
 
-    good_vals = np.array(
-        [
-            -0.958016797002,
-            1.0109751831,
-            2.96430606652,
-            0.313137860902,
-            4.59996300532,
-            0.99000982258,
-        ]
-    )
+    # fmt: off
+    good_vals = np.array([-0.941674, 1.013711, 2.725373, 0.301217,
+                          4.589078, 0.948576])
+    # fmt: on
 
-    np.testing.assert_allclose(good_vals, fit_vals)
+    np.testing.assert_allclose(good_vals, fit_vals, rtol=1e-5)