diff --git a/CLAUDE.md b/CLAUDE.md
index bc7f0b67..ea650582 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -143,8 +143,11 @@ Non-snapshot tests (logical assertions, error checks, etc.) run fine on any plat
 This is a known quirk — don't worry about these specific persistent failures. However, if you see more than ~3 snapshot failures, something real is likely broken and needs investigation.
 
 ### Running Tests
+
+The canonical test workflow is to open the devcontainer and run `make testall`. Do not attempt to run the full test suite outside the devcontainer — snapshot tests will fail due to font/rendering differences, and even non-snapshot tests may pull in snapshot comparisons.
+
 ```bash
-# Via Makefile
+# Via Makefile (inside devcontainer)
 make testall                                          # Run all tests
 make testone testfile="inst/tinytest/test-legend.R"   # Run single test file
 
diff --git a/R/tinyplot.R b/R/tinyplot.R
index f27cf80f..e15b1193 100644
--- a/R/tinyplot.R
+++ b/R/tinyplot.R
@@ -995,6 +995,7 @@ tinyplot.default = function(
       .bp = environment(.h)[["base_par"]]
       if (is.list(.bp)) .tpars = modifyList(.tpars, .bp)
     }
+    if (!is.null(.tpars[["mar"]])) .theme_mar = .tpars[["mar"]]
 
     # Detect outer-legend sides (order: bottom, left, top, right).
     .lgnd_pos = settings$legend_args[["x"]]
diff --git a/inst/tinytest/_tinysnapshot/tinytheme_dynmar_mar_override.svg b/inst/tinytest/_tinysnapshot/tinytheme_dynmar_mar_override.svg
new file mode 100644
index 00000000..94c2b225
--- /dev/null
+++ b/inst/tinytest/_tinysnapshot/tinytheme_dynmar_mar_override.svg
@@ -0,0 +1,80 @@
+<?xml version='1.0' encoding='UTF-8' ?>
+<svg xmlns='http://www.w3.org/2000/svg' xmlns:xlink='http://www.w3.org/1999/xlink' width='504.00pt' height='504.00pt' viewBox='0 0 504.00 504.00'>
+<g class='svglite'>
+<defs>
+  <style type='text/css'><![CDATA[
+    .svglite line, .svglite polyline, .svglite polygon, .svglite path, .svglite rect, .svglite circle {
+      fill: none;
+      stroke: #000000;
+      stroke-linecap: round;
+      stroke-linejoin: round;
+      stroke-miterlimit: 10.00;
+    }
+    .svglite text {
+      white-space: pre;
+    }
+    .svglite g.glyphgroup path {
+      fill: inherit;
+      stroke: none;
+    }
+  ]]></style>
+</defs>
+<rect width='100%' height='100%' style='stroke: none; fill: #FFFFFF;'/>
+<defs>
+  <clipPath id='cpMC4wMHw1MDQuMDB8MC4wMHw1MDQuMDA='>
+    <rect x='0.00' y='0.00' width='504.00' height='504.00' />
+  </clipPath>
+</defs>
+<g clip-path='url(#cpMC4wMHw1MDQuMDB8MC4wMHw1MDQuMDA=)'>
+<text x='118.08' y='83.81' style='font-size: 14.40px; font-weight: bold; font-family: "Liberation Sans";' textLength='144.75px' lengthAdjust='spacingAndGlyphs'>Custom mar override</text>
+<text x='275.04' y='429.12' text-anchor='middle' style='font-size: 12.00px; font-family: "Liberation Sans";' textLength='29.34px' lengthAdjust='spacingAndGlyphs'>Index</text>
+<text transform='translate(83.52,239.18) rotate(-90)' text-anchor='middle' style='font-size: 12.00px; font-family: "Liberation Sans";' textLength='23.34px' lengthAdjust='spacingAndGlyphs'>0:10</text>
+<line x1='158.77' y1='385.92' x2='391.31' y2='385.92' style='stroke-width: 0.75;' />
+<line x1='158.77' y1='385.92' x2='158.77' y2='390.24' style='stroke-width: 0.75;' />
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+<line x1='275.04' y1='385.92' x2='275.04' y2='390.24' style='stroke-width: 0.75;' />
+<line x1='333.17' y1='385.92' x2='333.17' y2='390.24' style='stroke-width: 0.75;' />
+<line x1='391.31' y1='385.92' x2='391.31' y2='390.24' style='stroke-width: 0.75;' />
+<text x='158.77' y='407.52' text-anchor='middle' style='font-size: 12.00px; font-family: "Liberation Sans";' textLength='6.67px' lengthAdjust='spacingAndGlyphs'>2</text>
+<text x='216.91' y='407.52' text-anchor='middle' style='font-size: 12.00px; font-family: "Liberation Sans";' textLength='6.67px' lengthAdjust='spacingAndGlyphs'>4</text>
+<text x='275.04' y='407.52' text-anchor='middle' style='font-size: 12.00px; font-family: "Liberation Sans";' textLength='6.67px' lengthAdjust='spacingAndGlyphs'>6</text>
+<text x='333.17' y='407.52' text-anchor='middle' style='font-size: 12.00px; font-family: "Liberation Sans";' textLength='6.67px' lengthAdjust='spacingAndGlyphs'>8</text>
+<text x='391.31' y='407.52' text-anchor='middle' style='font-size: 12.00px; font-family: "Liberation Sans";' textLength='13.34px' lengthAdjust='spacingAndGlyphs'>10</text>
+<line x1='118.08' y1='375.05' x2='118.08' y2='103.32' style='stroke-width: 0.75;' />
+<line x1='118.08' y1='375.05' x2='113.76' y2='375.05' style='stroke-width: 0.75;' />
+<line x1='118.08' y1='320.70' x2='113.76' y2='320.70' style='stroke-width: 0.75;' />
+<line x1='118.08' y1='266.36' x2='113.76' y2='266.36' style='stroke-width: 0.75;' />
+<line x1='118.08' y1='212.01' x2='113.76' y2='212.01' style='stroke-width: 0.75;' />
+<line x1='118.08' y1='157.66' x2='113.76' y2='157.66' style='stroke-width: 0.75;' />
+<line x1='118.08' y1='103.32' x2='113.76' y2='103.32' style='stroke-width: 0.75;' />
+<text x='108.00' y='379.18' text-anchor='end' style='font-size: 12.00px; font-family: "Liberation Sans";' textLength='6.67px' lengthAdjust='spacingAndGlyphs'>0</text>
+<text x='108.00' y='324.83' text-anchor='end' style='font-size: 12.00px; font-family: "Liberation Sans";' textLength='6.67px' lengthAdjust='spacingAndGlyphs'>2</text>
+<text x='108.00' y='270.49' text-anchor='end' style='font-size: 12.00px; font-family: "Liberation Sans";' textLength='6.67px' lengthAdjust='spacingAndGlyphs'>4</text>
+<text x='108.00' y='216.14' text-anchor='end' style='font-size: 12.00px; font-family: "Liberation Sans";' textLength='6.67px' lengthAdjust='spacingAndGlyphs'>6</text>
+<text x='108.00' y='161.79' text-anchor='end' style='font-size: 12.00px; font-family: "Liberation Sans";' textLength='6.67px' lengthAdjust='spacingAndGlyphs'>8</text>
+<text x='108.00' y='107.45' text-anchor='end' style='font-size: 12.00px; font-family: "Liberation Sans";' textLength='13.34px' lengthAdjust='spacingAndGlyphs'>10</text>
+<polygon points='118.08,385.92 432.00,385.92 432.00,92.45 118.08,92.45 ' style='stroke-width: 0.75;' />
+</g>
+<defs>
+  <clipPath id='cpMTE4LjA4fDQzMi4wMHw5Mi40NXwzODUuOTI='>
+    <rect x='118.08' y='92.45' width='313.92' height='293.47' />
+  </clipPath>
+</defs>
+<g clip-path='url(#cpMTE4LjA4fDQzMi4wMHw5Mi40NXwzODUuOTI=)'>
+<circle cx='129.71' cy='375.05' r='2.70' style='stroke-width: 0.75; stroke: none; fill: #000000;' />
+<circle cx='158.77' cy='347.88' r='2.70' style='stroke-width: 0.75; stroke: none; fill: #000000;' />
+<circle cx='187.84' cy='320.70' r='2.70' style='stroke-width: 0.75; stroke: none; fill: #000000;' />
+<circle cx='216.91' cy='293.53' r='2.70' style='stroke-width: 0.75; stroke: none; fill: #000000;' />
+<circle cx='245.97' cy='266.36' r='2.70' style='stroke-width: 0.75; stroke: none; fill: #000000;' />
+<circle cx='275.04' cy='239.18' r='2.70' style='stroke-width: 0.75; stroke: none; fill: #000000;' />
+<circle cx='304.11' cy='212.01' r='2.70' style='stroke-width: 0.75; stroke: none; fill: #000000;' />
+<circle cx='333.17' cy='184.84' r='2.70' style='stroke-width: 0.75; stroke: none; fill: #000000;' />
+<circle cx='362.24' cy='157.66' r='2.70' style='stroke-width: 0.75; stroke: none; fill: #000000;' />
+<circle cx='391.31' cy='130.49' r='2.70' style='stroke-width: 0.75; stroke: none; fill: #000000;' />
+<circle cx='420.37' cy='103.32' r='2.70' style='stroke-width: 0.75; stroke: none; fill: #000000;' />
+</g>
+<g clip-path='url(#cpMC4wMHw1MDQuMDB8MC4wMHw1MDQuMDA=)'>
+<polygon points='0.00,504.00 504.00,504.00 504.00,0.00 0.00,0.00 ' style='stroke-width: 0.75; stroke-dasharray: 4.00,4.00;' />
+</g>
+</g>
+</svg>
diff --git a/inst/tinytest/test-tinytheme.R b/inst/tinytest/test-tinytheme.R
index f71f8338..9584c772 100644
--- a/inst/tinytest/test-tinytheme.R
+++ b/inst/tinytest/test-tinytheme.R
@@ -178,3 +178,12 @@ f = function() {
   plt_add(type = "b")
 }
 expect_snapshot_plot(f, label = "ephemeral_default_theme_add")
+
+# User mar override respected under dynmar (#587)
+f = function() {
+  tinytheme("dynamic", mar = c(5, 5, 5, 5))
+  plt(0:10, main = "Custom mar override")
+  box("inner", lty = 2)
+  tinytheme()
+}
+expect_snapshot_plot(f, label = "tinytheme_dynmar_mar_override")