diff --git a/packages/mermaid/src/themes/theme-base.js b/packages/mermaid/src/themes/theme-base.js
index 01f8a9c0b..a3d4a738f 100644
--- a/packages/mermaid/src/themes/theme-base.js
+++ b/packages/mermaid/src/themes/theme-base.js
@@ -219,7 +219,7 @@ class Theme {
     /* requirement-diagram */
     this.requirementBackground = this.requirementBackground || this.primaryColor;
     this.requirementBorderColor = this.requirementBorderColor || this.primaryBorderColor;
-    this.requirementBorderSize = this.requirementBorderSize || this.primaryBorderColor;
+    this.requirementBorderSize = this.requirementBorderSize || '1';
     this.requirementTextColor = this.requirementTextColor || this.primaryTextColor;
     this.relationColor = this.relationColor || this.lineColor;
     this.relationLabelBackground =
diff --git a/packages/mermaid/src/themes/theme-dark.js b/packages/mermaid/src/themes/theme-dark.js
index 6ee26169d..8fde494bd 100644
--- a/packages/mermaid/src/themes/theme-dark.js
+++ b/packages/mermaid/src/themes/theme-dark.js
@@ -231,7 +231,7 @@ class Theme {
     /* requirement-diagram */
     this.requirementBackground = this.requirementBackground || this.primaryColor;
     this.requirementBorderColor = this.requirementBorderColor || this.primaryBorderColor;
-    this.requirementBorderSize = this.requirementBorderSize || this.primaryBorderColor;
+    this.requirementBorderSize = this.requirementBorderSize || '1';
     this.requirementTextColor = this.requirementTextColor || this.primaryTextColor;
     this.relationColor = this.relationColor || this.lineColor;
     this.relationLabelBackground =
diff --git a/packages/mermaid/src/themes/theme-default.js b/packages/mermaid/src/themes/theme-default.js
index 339bfa48a..460a1b920 100644
--- a/packages/mermaid/src/themes/theme-default.js
+++ b/packages/mermaid/src/themes/theme-default.js
@@ -250,7 +250,7 @@ class Theme {
     /* requirement-diagram */
     this.requirementBackground = this.requirementBackground || this.primaryColor;
     this.requirementBorderColor = this.requirementBorderColor || this.primaryBorderColor;
-    this.requirementBorderSize = this.requirementBorderSize || this.primaryBorderColor;
+    this.requirementBorderSize = this.requirementBorderSize || '1';
     this.requirementTextColor = this.requirementTextColor || this.primaryTextColor;
     this.relationColor = this.relationColor || this.lineColor;
     this.relationLabelBackground = this.relationLabelBackground || this.labelBackground;
diff --git a/packages/mermaid/src/themes/theme-forest.js b/packages/mermaid/src/themes/theme-forest.js
index 3d47684bc..527c6a38c 100644
--- a/packages/mermaid/src/themes/theme-forest.js
+++ b/packages/mermaid/src/themes/theme-forest.js
@@ -219,7 +219,7 @@ class Theme {
     /* requirement-diagram */
     this.requirementBackground = this.requirementBackground || this.primaryColor;
     this.requirementBorderColor = this.requirementBorderColor || this.primaryBorderColor;
-    this.requirementBorderSize = this.requirementBorderSize || this.primaryBorderColor;
+    this.requirementBorderSize = this.requirementBorderSize || '1';
     this.requirementTextColor = this.requirementTextColor || this.primaryTextColor;
     this.relationColor = this.relationColor || this.lineColor;
     this.relationLabelBackground = this.relationLabelBackground || this.edgeLabelBackground;
diff --git a/packages/mermaid/src/themes/theme-neutral.js b/packages/mermaid/src/themes/theme-neutral.js
index 9dce63b8d..15c3d1d2d 100644
--- a/packages/mermaid/src/themes/theme-neutral.js
+++ b/packages/mermaid/src/themes/theme-neutral.js
@@ -249,7 +249,7 @@ class Theme {
     /* requirement-diagram */
     this.requirementBackground = this.requirementBackground || this.primaryColor;
     this.requirementBorderColor = this.requirementBorderColor || this.primaryBorderColor;
-    this.requirementBorderSize = this.requirementBorderSize || this.primaryBorderColor;
+    this.requirementBorderSize = this.requirementBorderSize || '1';
     this.requirementTextColor = this.requirementTextColor || this.primaryTextColor;
     this.relationColor = this.relationColor || this.lineColor;
     this.relationLabelBackground = this.relationLabelBackground || this.edgeLabelBackground;